From 266332a0527b67ec76d0ab038bb278a234b54606 Mon Sep 17 00:00:00 2001
From: Daniel Tschinder <daniel@tschinder.de>
Date: Tue, 14 Feb 2017 14:53:53 +0100
Subject: [PATCH] Merge master into 7.0 (#5310)

* Add new flow preset (#5288)

* Fix PathHoister hoisting JSX member expressions on "this". (#5143)

The PathHoister ignored member references on "this", causing it
to potentially hoist an expression above its function scope.

This patch tells the hoister to watch for "this", and if seen,
mark the nearest non-arrow function scope as the upper limit
for hoistng.

This fixes #4397 and is an alternative to #4787.

* Fix PathHoister hoisting before bindings. (#5153)

Fixes #5149 and enables a few additional safe hoists.

* Fix linting error

* feature: Support pure expressions in transform-react-constant-elements (#4812)

* Fix loose for-of with label (#5298)

* Rewrite Hub as interface #5047 (#5050)

* Rewrite Hub as interface #5047

* Update index.js

* Avoid adding unnecessary closure for block scoping (#5246)

When you write

```
for (const x of l) {
  setTimeout(() => x);
}
```

we need to add a closure because the variable is meant to be block-scoped and recreated each time the block runs. We do this.

However, we also add the closure when no loop is present. This isn't necessary, because if no loop is present then each piece of code runs at most once. I changed the transform to only add a closure if a variable is referenced from within a loop.

* Add greenkeeperio-bot to mention-bot blacklist (#5301) [skip ci]

* Upgrade lerna to current beta. (#5300)

* Revert "Upgrade lerna to current beta." (#5303)

* Add charset so tests work with convert-source-map@>1.4 (#5302)

* Add CHANGELOG for 6.23.0 [skip ci] (#5304)

* Update babel-types README from script.

* v6.23.0

* Revert change that lerna force-committed.

* Revert "Rewrite Hub as interface #5047" (#5306)

* v6.23.1

* Revert lerna again
---
 .mention-bot                                  |  8 +-
 CHANGELOG.md                                  | 90 +++++++++++++++++++
 packages/babel-cli/package.json               |  8 +-
 packages/babel-core/package.json              | 20 ++---
 .../misc/regression-2364/actual.js            |  2 +-
 .../misc/regression-2364/expected.js          | 22 ++---
 .../source-maps/inline/expected.js            |  2 +-
 packages/babel-generator/package.json         |  8 +-
 .../package.json                              |  4 +-
 packages/babel-helper-define-map/package.json |  6 +-
 .../babel-helper-function-name/package.json   |  8 +-
 .../package.json                              |  4 +-
 .../babel-helper-replace-supers/package.json  | 12 +--
 .../package.json                              |  6 +-
 packages/babel-helpers/package.json           |  4 +-
 packages/babel-messages/package.json          |  2 +-
 .../package.json                              |  6 +-
 .../package.json                              |  8 +-
 .../src/index.js                              | 27 +++++-
 .../fixtures/general/issue-2174/expected.js   | 14 ++-
 .../general/loops-and-no-loops/actual.js      | 34 +++++++
 .../general/loops-and-no-loops/expected.js    | 42 +++++++++
 .../fixtures/general/sibling-scopes/actual.js | 11 +++
 .../general/sibling-scopes/expected.js        | 15 ++++
 .../fixtures/general/superswitch/actual.js    | 24 ++---
 .../fixtures/general/superswitch/expected.js  | 46 +++++-----
 .../general/switch-callbacks/actual.js        | 14 +--
 .../general/switch-callbacks/expected.js      | 26 +++---
 .../for-const-closure/expected.js             |  6 ++
 .../superswitch/actual.js                     | 16 ----
 .../superswitch/options.json                  |  3 -
 .../package.json                              | 18 ++--
 .../package.json                              |  2 +-
 .../package.json                              |  2 +-
 .../src/index.js                              | 18 ++--
 .../loose/nested-label-for-of/actual.js       |  5 ++
 .../loose/nested-label-for-of/expected.js     | 31 +++++++
 .../package.json                              |  6 +-
 .../package.json                              |  4 +-
 .../package.json                              |  4 +-
 .../package.json                              |  8 +-
 .../package.json                              |  2 +-
 .../package.json                              |  2 +-
 .../package.json                              |  2 +-
 .../package.json                              |  2 +-
 .../src/index.js                              | 28 +++++-
 .../expected.js                               | 17 ++--
 .../expected.js                               | 18 ++--
 .../dont-hoist-before-class/actual.js         | 15 ++++
 .../dont-hoist-before-class/expected.js       | 13 +++
 .../dont-hoist-before-declaration/expected.js |  5 +-
 .../dont-hoist-before-hoc/actual.js           | 18 ++++
 .../dont-hoist-before-hoc/expected.js         | 18 ++++
 .../expected.js                               | 14 +--
 .../member-expression-constant/actual.js      |  4 +
 .../member-expression-constant/expected.js    |  7 ++
 .../member-expression-this/actual.js          |  5 ++
 .../member-expression-this/expected.js        | 12 +++
 .../member-expression-this/options.json       |  3 +
 .../member-expression/actual.js               |  6 ++
 .../member-expression/expected.js             | 16 ++++
 .../member-expression/options.json            |  3 +
 .../constant-elements/pure-deopt/actual.js    |  5 ++
 .../constant-elements/pure-deopt/expected.js  |  5 ++
 .../pure-expression-2/actual.js               |  5 ++
 .../pure-expression-2/expected.js             |  8 ++
 .../pure-expression-3/actual.js               | 10 +++
 .../pure-expression-3/expected.js             | 10 +++
 .../pure-expression/actual.js                 | 11 +++
 .../pure-expression/expected.js               |  8 ++
 .../package.json                              |  2 +-
 .../package.json                              |  4 +-
 .../package.json                              |  2 +-
 packages/babel-polyfill/package.json          |  2 +-
 packages/babel-preset-flow/.npmignore         |  3 +
 packages/babel-preset-flow/README.md          | 53 +++++++++++
 packages/babel-preset-flow/package.json       | 18 ++++
 packages/babel-preset-flow/src/index.js       |  7 ++
 packages/babel-preset-react/README.md         |  5 +-
 packages/babel-preset-react/package.json      |  9 +-
 packages/babel-preset-react/src/index.js      |  8 +-
 packages/babel-register/package.json          |  4 +-
 packages/babel-template/package.json          |  6 +-
 packages/babel-traverse/package.json          |  8 +-
 .../babel-traverse/src/path/lib/hoister.js    | 80 ++++++++++++-----
 packages/babel-types/README.md                |  1 +
 packages/babel-types/package.json             |  2 +-
 87 files changed, 828 insertions(+), 254 deletions(-)
 create mode 100644 packages/babel-plugin-transform-es2015-block-scoping/test/fixtures/general/loops-and-no-loops/actual.js
 create mode 100644 packages/babel-plugin-transform-es2015-block-scoping/test/fixtures/general/loops-and-no-loops/expected.js
 create mode 100644 packages/babel-plugin-transform-es2015-block-scoping/test/fixtures/general/sibling-scopes/actual.js
 create mode 100644 packages/babel-plugin-transform-es2015-block-scoping/test/fixtures/general/sibling-scopes/expected.js
 create mode 100644 packages/babel-plugin-transform-es2015-block-scoping/test/fixtures/throwIfClosureRequired/for-const-closure/expected.js
 delete mode 100644 packages/babel-plugin-transform-es2015-block-scoping/test/fixtures/throwIfClosureRequired/superswitch/actual.js
 delete mode 100644 packages/babel-plugin-transform-es2015-block-scoping/test/fixtures/throwIfClosureRequired/superswitch/options.json
 create mode 100644 packages/babel-plugin-transform-es2015-for-of/test/fixtures/loose/nested-label-for-of/actual.js
 create mode 100644 packages/babel-plugin-transform-es2015-for-of/test/fixtures/loose/nested-label-for-of/expected.js
 create mode 100644 packages/babel-plugin-transform-react-constant-elements/test/fixtures/constant-elements/dont-hoist-before-class/actual.js
 create mode 100644 packages/babel-plugin-transform-react-constant-elements/test/fixtures/constant-elements/dont-hoist-before-class/expected.js
 create mode 100644 packages/babel-plugin-transform-react-constant-elements/test/fixtures/constant-elements/dont-hoist-before-hoc/actual.js
 create mode 100644 packages/babel-plugin-transform-react-constant-elements/test/fixtures/constant-elements/dont-hoist-before-hoc/expected.js
 create mode 100644 packages/babel-plugin-transform-react-constant-elements/test/fixtures/constant-elements/member-expression-constant/actual.js
 create mode 100644 packages/babel-plugin-transform-react-constant-elements/test/fixtures/constant-elements/member-expression-constant/expected.js
 create mode 100644 packages/babel-plugin-transform-react-constant-elements/test/fixtures/constant-elements/member-expression-this/actual.js
 create mode 100644 packages/babel-plugin-transform-react-constant-elements/test/fixtures/constant-elements/member-expression-this/expected.js
 create mode 100644 packages/babel-plugin-transform-react-constant-elements/test/fixtures/constant-elements/member-expression-this/options.json
 create mode 100644 packages/babel-plugin-transform-react-constant-elements/test/fixtures/constant-elements/member-expression/actual.js
 create mode 100644 packages/babel-plugin-transform-react-constant-elements/test/fixtures/constant-elements/member-expression/expected.js
 create mode 100644 packages/babel-plugin-transform-react-constant-elements/test/fixtures/constant-elements/member-expression/options.json
 create mode 100644 packages/babel-plugin-transform-react-constant-elements/test/fixtures/constant-elements/pure-deopt/actual.js
 create mode 100644 packages/babel-plugin-transform-react-constant-elements/test/fixtures/constant-elements/pure-deopt/expected.js
 create mode 100644 packages/babel-plugin-transform-react-constant-elements/test/fixtures/constant-elements/pure-expression-2/actual.js
 create mode 100644 packages/babel-plugin-transform-react-constant-elements/test/fixtures/constant-elements/pure-expression-2/expected.js
 create mode 100644 packages/babel-plugin-transform-react-constant-elements/test/fixtures/constant-elements/pure-expression-3/actual.js
 create mode 100644 packages/babel-plugin-transform-react-constant-elements/test/fixtures/constant-elements/pure-expression-3/expected.js
 create mode 100644 packages/babel-plugin-transform-react-constant-elements/test/fixtures/constant-elements/pure-expression/actual.js
 create mode 100644 packages/babel-plugin-transform-react-constant-elements/test/fixtures/constant-elements/pure-expression/expected.js
 create mode 100644 packages/babel-preset-flow/.npmignore
 create mode 100644 packages/babel-preset-flow/README.md
 create mode 100644 packages/babel-preset-flow/package.json
 create mode 100644 packages/babel-preset-flow/src/index.js

diff --git a/.mention-bot b/.mention-bot
index 32b2d0479e72..671103a31cd8 100644
--- a/.mention-bot
+++ b/.mention-bot
@@ -1,5 +1,11 @@
 {
-  "userBlacklist": [ "amasad", "thejameskyle", "jmm", "kittens" ],
+  "userBlacklist": [
+    "amasad",
+    "greenkeeperio-bot",
+    "jmm",
+    "kittens",
+    "thejameskyle"
+   ],
   "fileBlacklist": ["*.md"],
   "skipAlreadyAssignedPR": true,
   "createReviewRequest": true
diff --git a/CHANGELOG.md b/CHANGELOG.md
index 7ff3de0e5146..96d28278e150 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -13,6 +13,96 @@ _Note: Gaps between patch versions are faulty, broken or test releases._
 
 See [CHANGELOG - 6to5](CHANGELOG-6to5.md) for the pre-4.0.0 version changelog.
 
+## 6.23.0 (2017-02-13)
+
+#### :rocket: New Feature
+* `babel-plugin-transform-react-constant-elements`
+  * [#4812](https://github.com/babel/babel/pull/4812) feature: Support pure expressions in transform-react-constant-elements. ([@STRML](https://github.com/STRML))
+* `babel-preset-flow`, `babel-preset-react`
+  * [#5288](https://github.com/babel/babel/pull/5288) Add new flow preset. ([@thejameskyle](https://github.com/thejameskyle))
+* `babel-traverse`
+  * [#5230](https://github.com/babel/babel/pull/5230) Add path/family sibling traversal methods. ([@chitchu](https://github.com/chitchu))
+* `babel-plugin-transform-es2015-block-scoping`
+  * [#5236](https://github.com/babel/babel/pull/5236) Add option to block-scoping to throw on slow code. ([@spicyj](https://github.com/spicyj))
+
+#### :bug: Bug Fix
+* `babel-core`, `babel-traverse`
+  * [#5050](https://github.com/babel/babel/pull/5050) Rewrite Hub as interface #5047. ([@yongxu](https://github.com/yongxu))
+* `babel-plugin-transform-es2015-for-of`
+  * [#5298](https://github.com/babel/babel/pull/5298) Fix loose for-of with label. ([@jridgewell](https://github.com/jridgewell))
+* `babel-plugin-transform-react-constant-elements`, `babel-traverse`
+  * [#5153](https://github.com/babel/babel/pull/5153) Fix react constant elements bindings. ([@STRML](https://github.com/STRML))
+  * [#5143](https://github.com/babel/babel/pull/5143) Fix PathHoister hoisting JSX member expressions on "this".. ([@STRML](https://github.com/STRML))
+* `babel-plugin-transform-do-expressions`, `babel-traverse`
+  * [#5030](https://github.com/babel/babel/pull/5030) Prevent multiple return statements in a loop when replacing expressions. ([@existentialism](https://github.com/existentialism))
+* `babel-register`
+  * [#5260](https://github.com/babel/babel/pull/5260) Fix TypeError with babel-register's cache. ([@xtuc](https://github.com/xtuc))
+* `babel-traverse`
+  * [#5206](https://github.com/babel/babel/pull/5206) Deopt evaluation of undefined with a local binding. Closes [#5204](https://github.com/babel/babel/issues/5204). ([@boopathi](https://github.com/boopathi))
+* `babel-plugin-transform-runtime`
+  * [#5195](https://github.com/babel/babel/pull/5195) Don't transpile ES7 symbol properties. ([@taion](https://github.com/taion))
+* `babel`
+  * [#5258](https://github.com/babel/babel/pull/5258) checks if babel is installed globally and displays correct cli message. ([@xtina-starr](https://github.com/xtina-starr))
+* `babel-generator`
+  * [#5270](https://github.com/babel/babel/pull/5270) Emit parens for await of ternary expressions. ([@erikdesjardins](https://github.com/erikdesjardins))
+  * [#5193](https://github.com/babel/babel/pull/5193) Fix missing parens when function expressions is tag. ([@existentialism](https://github.com/existentialism))
+* `babel-plugin-transform-es2015-modules-commonjs`
+  * [#5235](https://github.com/babel/babel/pull/5235) Limit export node default assignment stack size #4323. ([@mattste](https://github.com/mattste))
+
+#### :memo: Documentation
+* `babel-*`
+  * [#5244](https://github.com/babel/babel/pull/5244) Normalize options sections in docs [skip ci]. ([@existentialism](https://github.com/existentialism))
+  * [#5216](https://github.com/babel/babel/pull/5216) Remove link to REPL. ([@xtuc](https://github.com/xtuc))
+* Other
+  * [#5242](https://github.com/babel/babel/pull/5242) Add our business model [skip ci]. ([@hzoo](https://github.com/hzoo))
+* `babel-plugin-transform-es2015-spread`
+  * [#5227](https://github.com/babel/babel/pull/5227) Add example to spread README [skip ci]. ([@finkef](https://github.com/finkef))
+* `babel-plugin-transform-flow-strip-types`
+  * [#5212](https://github.com/babel/babel/pull/5212) Remove REPL link transform-flow-strip-types doc. ([@xtuc](https://github.com/xtuc))
+* `babel-plugin-transform-regenerator`
+  * [#5202](https://github.com/babel/babel/pull/5202) Fix transform-regenerator README. ([@xtuc](https://github.com/xtuc))
+* `babel-plugin-transform-es2015-arrow-functions`
+  * [#5200](https://github.com/babel/babel/pull/5200) Fix transform-es2015-arrow-functions code blocks on the website. ([@xtuc](https://github.com/xtuc))
+  * [#5194](https://github.com/babel/babel/pull/5194) Fix transform-es2015-arrow-functions README. ([@xtuc](https://github.com/xtuc))
+
+#### :house: Internal
+* `babel-core`
+  * [#5302](https://github.com/babel/babel/pull/5302) Add charset so tests work with convert-source-map@>1.4. ([@loganfsmyth](https://github.com/loganfsmyth))
+* `babel-core`, `babel-traverse`
+  * [#5050](https://github.com/babel/babel/pull/5050) Rewrite Hub as interface #5047. ([@yongxu](https://github.com/yongxu))
+* `babel-generator`
+  * [#5255](https://github.com/babel/babel/pull/5255) codegen performance: use trim instead of lodash/trimEnd. ([@jwbay](https://github.com/jwbay))
+* `babel-types`
+  * [#5181](https://github.com/babel/babel/pull/5181) Remove uses of lodash/compact. ([@zertosh](https://github.com/zertosh))
+* `babel-*`
+  * [#5265](https://github.com/babel/babel/pull/5265) Re-enable the max-len ESLint rule.. ([@loganfsmyth](https://github.com/loganfsmyth))
+* Other
+  * [#5264](https://github.com/babel/babel/pull/5264) Add a sublime project file. ([@loganfsmyth](https://github.com/loganfsmyth))
+  * [#5182](https://github.com/babel/babel/pull/5182) Run coverage only once. ([@existentialism](https://github.com/existentialism))
+  * [#5165](https://github.com/babel/babel/pull/5165) Add Node 7 to CI. ([@chicoxyzzy](https://github.com/chicoxyzzy))
+
+#### Committers: 20
+- Andres Suarez ([zertosh](https://github.com/zertosh))
+- Ben Alpert ([spicyj](https://github.com/spicyj))
+- Boopathi Rajaa ([boopathi](https://github.com/boopathi))
+- Brian Ng ([existentialism](https://github.com/existentialism))
+- Christina ([xtina-starr](https://github.com/xtina-starr))
+- Erik Desjardins ([erikdesjardins](https://github.com/erikdesjardins))
+- Fabian Finke ([finkef](https://github.com/finkef))
+- Henry Zhu ([hzoo](https://github.com/hzoo))
+- Jimmy Jia ([taion](https://github.com/taion))
+- Justin Ridgewell ([jridgewell](https://github.com/jridgewell))
+- Logan Smyth ([loganfsmyth](https://github.com/loganfsmyth))
+- Matt Stewart ([mattste](https://github.com/mattste))
+- Samuel Reed ([STRML](https://github.com/STRML))
+- Sergey Rubanov ([chicoxyzzy](https://github.com/chicoxyzzy))
+- Sven SAULEAU ([xtuc](https://github.com/xtuc))
+- Vicente Jr Yuchitcho ([chitchu](https://github.com/chitchu))
+- Yongxu Ren ([yongxu](https://github.com/yongxu))
+- [jwbay](https://github.com/jwbay)
+- james kyle ([thejameskyle](https://github.com/thejameskyle))
+- Łukasz Lityński ([hex13](https://github.com/hex13))
+
 ## 6.22.2 (2017-01-19)
 
 #### :bug: Bug Fix
diff --git a/packages/babel-cli/package.json b/packages/babel-cli/package.json
index dba5eea05a4d..f836c0d113d5 100644
--- a/packages/babel-cli/package.json
+++ b/packages/babel-cli/package.json
@@ -1,6 +1,6 @@
 {
   "name": "babel-cli",
-  "version": "6.22.2",
+  "version": "6.23.0",
   "description": "Babel command line.",
   "author": "Sebastian McKenzie <sebmck@gmail.com>",
   "homepage": "https://babeljs.io/",
@@ -16,9 +16,9 @@
     "compiler"
   ],
   "dependencies": {
-    "babel-core": "^6.22.1",
-    "babel-register": "^6.22.0",
-    "babel-polyfill": "^6.22.0",
+    "babel-core": "^6.23.0",
+    "babel-register": "^6.23.0",
+    "babel-polyfill": "^6.23.0",
     "commander": "^2.8.1",
     "convert-source-map": "^1.1.0",
     "fs-readdir-recursive": "^1.0.0",
diff --git a/packages/babel-core/package.json b/packages/babel-core/package.json
index e28bf0b3c70f..4e44376e714f 100644
--- a/packages/babel-core/package.json
+++ b/packages/babel-core/package.json
@@ -1,6 +1,6 @@
 {
   "name": "babel-core",
-  "version": "6.22.1",
+  "version": "6.23.1",
   "description": "Babel compiler core.",
   "author": "Sebastian McKenzie <sebmck@gmail.com>",
   "homepage": "https://babeljs.io/",
@@ -27,13 +27,13 @@
   },
   "dependencies": {
     "babel-code-frame": "^6.22.0",
-    "babel-generator": "^6.22.0",
-    "babel-helpers": "^6.22.0",
-    "babel-messages": "^6.22.0",
-    "babel-template": "^6.22.0",
-    "babel-register": "^6.22.0",
-    "babel-traverse": "^6.22.1",
-    "babel-types": "^6.22.0",
+    "babel-generator": "^6.23.0",
+    "babel-helpers": "^6.23.0",
+    "babel-messages": "^6.23.0",
+    "babel-template": "^6.23.0",
+    "babel-register": "^6.23.0",
+    "babel-traverse": "^6.23.1",
+    "babel-types": "^6.23.0",
     "babylon": "^6.11.0",
     "convert-source-map": "^1.1.0",
     "debug": "^2.1.1",
@@ -46,7 +46,7 @@
   },
   "devDependencies": {
     "babel-helper-fixtures": "^6.22.0",
-    "babel-helper-transform-fixture-test-runner": "^6.22.0",
-    "babel-polyfill": "^6.22.0"
+    "babel-helper-transform-fixture-test-runner": "^6.23.0",
+    "babel-polyfill": "^6.23.0"
   }
 }
diff --git a/packages/babel-core/test/fixtures/transformation/misc/regression-2364/actual.js b/packages/babel-core/test/fixtures/transformation/misc/regression-2364/actual.js
index e995e0d23496..c2ae386b34dd 100644
--- a/packages/babel-core/test/fixtures/transformation/misc/regression-2364/actual.js
+++ b/packages/babel-core/test/fixtures/transformation/misc/regression-2364/actual.js
@@ -1,6 +1,6 @@
 function wrapper(fn) {
   return (...args) => {
-    if (someCondition) {
+    while (someCondition) {
       const val = fn(...args);
       return val.test(() => {
         console.log(val);
diff --git a/packages/babel-core/test/fixtures/transformation/misc/regression-2364/expected.js b/packages/babel-core/test/fixtures/transformation/misc/regression-2364/expected.js
index ae32dbb4d39a..c1079c01cbbf 100644
--- a/packages/babel-core/test/fixtures/transformation/misc/regression-2364/expected.js
+++ b/packages/babel-core/test/fixtures/transformation/misc/regression-2364/expected.js
@@ -2,17 +2,19 @@ function wrapper(fn) {
   return function () {
     var _arguments = arguments;
 
-    if (someCondition) {
-      var _ret = function () {
-        var val = fn(..._arguments);
-        return {
-          v: val.test(function () {
-            console.log(val);
-          })
-        };
-      }();
+    var _loop = function () {
+      var val = fn(..._arguments);
+      return {
+        v: val.test(function () {
+          console.log(val);
+        })
+      };
+    };
+
+    while (someCondition) {
+      var _ret = _loop();
 
       if (typeof _ret === "object") return _ret.v;
     }
   };
-}
\ No newline at end of file
+}
diff --git a/packages/babel-core/test/fixtures/transformation/source-maps/inline/expected.js b/packages/babel-core/test/fixtures/transformation/source-maps/inline/expected.js
index 00ae47b8755d..991056b8bf3a 100644
--- a/packages/babel-core/test/fixtures/transformation/source-maps/inline/expected.js
+++ b/packages/babel-core/test/fixtures/transformation/source-maps/inline/expected.js
@@ -1,4 +1,4 @@
 arr.map(function (x) {
   return x * x;
 });
-//# sourceMappingURL=data:application/json;base64,eyJ2ZXJzaW9uIjozLCJzb3VyY2VzIjpbInNvdXJjZS1tYXBzL2lubGluZS9hY3R1YWwuanMiXSwibmFtZXMiOlsiYXJyIiwibWFwIiwieCJdLCJtYXBwaW5ncyI6IkFBQUFBLElBQUlDLEdBQUosQ0FBUTtBQUFBLFNBQUtDLElBQUlBLENBQVQ7QUFBQSxDQUFSIiwiZmlsZSI6InNvdXJjZS1tYXBzL2lubGluZS9leHBlY3RlZC5qcyIsInNvdXJjZXNDb250ZW50IjpbImFyci5tYXAoeCA9PiB4ICogeCk7Il19
+//# sourceMappingURL=data:application/json;charset=utf-8;base64,eyJ2ZXJzaW9uIjozLCJzb3VyY2VzIjpbInNvdXJjZS1tYXBzL2lubGluZS9hY3R1YWwuanMiXSwibmFtZXMiOlsiYXJyIiwibWFwIiwieCJdLCJtYXBwaW5ncyI6IkFBQUFBLElBQUlDLEdBQUosQ0FBUTtBQUFBLFNBQUtDLElBQUlBLENBQVQ7QUFBQSxDQUFSIiwiZmlsZSI6InNvdXJjZS1tYXBzL2lubGluZS9leHBlY3RlZC5qcyIsInNvdXJjZXNDb250ZW50IjpbImFyci5tYXAoeCA9PiB4ICogeCk7Il19
diff --git a/packages/babel-generator/package.json b/packages/babel-generator/package.json
index 7e5511e36725..e45347d97446 100644
--- a/packages/babel-generator/package.json
+++ b/packages/babel-generator/package.json
@@ -1,6 +1,6 @@
 {
   "name": "babel-generator",
-  "version": "6.22.0",
+  "version": "6.23.0",
   "description": "Turns an AST into code.",
   "author": "Sebastian McKenzie <sebmck@gmail.com>",
   "homepage": "https://babeljs.io/",
@@ -11,9 +11,9 @@
     "lib"
   ],
   "dependencies": {
-    "babel-messages": "^6.22.0",
-    "babel-types": "^6.22.0",
-    "detect-indent": "^5.0.0",
+    "babel-messages": "^6.23.0",
+    "babel-types": "^6.23.0",
+    "detect-indent": "^4.0.0",
     "jsesc": "^1.3.0",
     "lodash": "^4.2.0",
     "source-map": "^0.5.0",
diff --git a/packages/babel-helper-builder-react-jsx/package.json b/packages/babel-helper-builder-react-jsx/package.json
index b42a80759e2f..cbeceb179c0f 100644
--- a/packages/babel-helper-builder-react-jsx/package.json
+++ b/packages/babel-helper-builder-react-jsx/package.json
@@ -1,12 +1,12 @@
 {
   "name": "babel-helper-builder-react-jsx",
-  "version": "6.22.0",
+  "version": "6.23.0",
   "description": "Helper function to build react jsx",
   "repository": "https://github.com/babel/babel/tree/master/packages/babel-helper-builder-react-jsx",
   "license": "MIT",
   "main": "lib/index.js",
   "dependencies": {
-    "babel-types": "^6.22.0",
+    "babel-types": "^6.23.0",
     "esutils": "^2.0.0",
     "lodash": "^4.2.0"
   }
diff --git a/packages/babel-helper-define-map/package.json b/packages/babel-helper-define-map/package.json
index 6b3757805046..c16bb59384e0 100644
--- a/packages/babel-helper-define-map/package.json
+++ b/packages/babel-helper-define-map/package.json
@@ -1,13 +1,13 @@
 {
   "name": "babel-helper-define-map",
-  "version": "6.22.0",
+  "version": "6.23.0",
   "description": "Helper function to define a map",
   "repository": "https://github.com/babel/babel/tree/master/packages/babel-helper-define-map",
   "license": "MIT",
   "main": "lib/index.js",
   "dependencies": {
     "lodash": "^4.2.0",
-    "babel-types": "^6.22.0",
-    "babel-helper-function-name": "^6.22.0"
+    "babel-types": "^6.23.0",
+    "babel-helper-function-name": "^6.23.0"
   }
 }
diff --git a/packages/babel-helper-function-name/package.json b/packages/babel-helper-function-name/package.json
index e73131de5d40..62c9f9373f57 100644
--- a/packages/babel-helper-function-name/package.json
+++ b/packages/babel-helper-function-name/package.json
@@ -1,14 +1,14 @@
 {
   "name": "babel-helper-function-name",
-  "version": "6.22.0",
+  "version": "6.23.0",
   "description": "Helper function to change the property 'name' of every function",
   "repository": "https://github.com/babel/babel/tree/master/packages/babel-helper-function-name",
   "license": "MIT",
   "main": "lib/index.js",
   "dependencies": {
-    "babel-types": "^6.22.0",
-    "babel-traverse": "^6.22.0",
+    "babel-types": "^6.23.0",
+    "babel-traverse": "^6.23.0",
     "babel-helper-get-function-arity": "^6.22.0",
-    "babel-template": "^6.22.0"
+    "babel-template": "^6.23.0"
   }
 }
diff --git a/packages/babel-helper-optimise-call-expression/package.json b/packages/babel-helper-optimise-call-expression/package.json
index b3b8cbdcb467..80e1f3424228 100644
--- a/packages/babel-helper-optimise-call-expression/package.json
+++ b/packages/babel-helper-optimise-call-expression/package.json
@@ -1,11 +1,11 @@
 {
   "name": "babel-helper-optimise-call-expression",
-  "version": "6.22.0",
+  "version": "6.23.0",
   "description": "Helper function to optimise call expression",
   "repository": "https://github.com/babel/babel/tree/master/packages/babel-helper-optimise-call-expression",
   "license": "MIT",
   "main": "lib/index.js",
   "dependencies": {
-    "babel-types": "^6.22.0"
+    "babel-types": "^6.23.0"
   }
 }
diff --git a/packages/babel-helper-replace-supers/package.json b/packages/babel-helper-replace-supers/package.json
index d1bb2832095b..24edb8200270 100644
--- a/packages/babel-helper-replace-supers/package.json
+++ b/packages/babel-helper-replace-supers/package.json
@@ -1,15 +1,15 @@
 {
   "name": "babel-helper-replace-supers",
-  "version": "6.22.0",
+  "version": "6.23.0",
   "description": "Helper function to replace supers",
   "repository": "https://github.com/babel/babel/tree/master/packages/babel-helper-replace-supers",
   "license": "MIT",
   "main": "lib/index.js",
   "dependencies": {
-    "babel-helper-optimise-call-expression": "^6.22.0",
-    "babel-traverse": "^6.22.0",
-    "babel-messages": "^6.22.0",
-    "babel-template": "^6.22.0",
-    "babel-types": "^6.22.0"
+    "babel-helper-optimise-call-expression": "^6.23.0",
+    "babel-traverse": "^6.23.0",
+    "babel-messages": "^6.23.0",
+    "babel-template": "^6.23.0",
+    "babel-types": "^6.23.0"
   }
 }
diff --git a/packages/babel-helper-transform-fixture-test-runner/package.json b/packages/babel-helper-transform-fixture-test-runner/package.json
index 2d9f78097a93..f5c03762893e 100644
--- a/packages/babel-helper-transform-fixture-test-runner/package.json
+++ b/packages/babel-helper-transform-fixture-test-runner/package.json
@@ -1,6 +1,6 @@
 {
   "name": "babel-helper-transform-fixture-test-runner",
-  "version": "6.22.0",
+  "version": "6.23.0",
   "description": "Transform test runner for babel-helper-fixtures module",
   "author": "Sebastian McKenzie <sebmck@gmail.com>",
   "homepage": "https://babeljs.io/",
@@ -8,8 +8,8 @@
   "repository": "https://github.com/babel/babel/tree/master/packages/babel-helper-transform-fixture-test-runner",
   "main": "lib/index.js",
   "dependencies": {
-    "babel-core": "^6.22.0",
-    "babel-polyfill": "^6.22.0",
+    "babel-core": "^6.23.0",
+    "babel-polyfill": "^6.23.0",
     "babel-helper-fixtures": "^6.22.0",
     "source-map": "^0.5.0",
     "babel-code-frame": "^6.22.0",
diff --git a/packages/babel-helpers/package.json b/packages/babel-helpers/package.json
index 19e03ccd865d..bc88144c05e4 100644
--- a/packages/babel-helpers/package.json
+++ b/packages/babel-helpers/package.json
@@ -1,6 +1,6 @@
 {
   "name": "babel-helpers",
-  "version": "6.22.0",
+  "version": "6.23.0",
   "description": "Collection of helper functions used by Babel transforms.",
   "author": "Sebastian McKenzie <sebmck@gmail.com>",
   "homepage": "https://babeljs.io/",
@@ -8,6 +8,6 @@
   "repository": "https://github.com/babel/babel/tree/master/packages/babel-helpers",
   "main": "lib/index.js",
   "dependencies": {
-    "babel-template": "^6.22.0"
+    "babel-template": "^6.23.0"
   }
 }
diff --git a/packages/babel-messages/package.json b/packages/babel-messages/package.json
index 022d7508ac37..177efb0499df 100644
--- a/packages/babel-messages/package.json
+++ b/packages/babel-messages/package.json
@@ -1,6 +1,6 @@
 {
   "name": "babel-messages",
-  "version": "6.22.0",
+  "version": "6.23.0",
   "description": "Collection of debug messages used by Babel.",
   "author": "Sebastian McKenzie <sebmck@gmail.com>",
   "homepage": "https://babeljs.io/",
diff --git a/packages/babel-plugin-transform-class-properties/package.json b/packages/babel-plugin-transform-class-properties/package.json
index 7122b69b1065..8f0b3d74cd28 100644
--- a/packages/babel-plugin-transform-class-properties/package.json
+++ b/packages/babel-plugin-transform-class-properties/package.json
@@ -1,6 +1,6 @@
 {
   "name": "babel-plugin-transform-class-properties",
-  "version": "6.22.0",
+  "version": "6.23.0",
   "description": "This plugin transforms static class properties as well as properties declared with the property initializer syntax",
   "repository": "https://github.com/babel/babel/tree/master/packages/babel-plugin-transform-class-properties",
   "license": "MIT",
@@ -9,9 +9,9 @@
     "babel-plugin"
   ],
   "dependencies": {
-    "babel-helper-function-name": "^6.22.0",
+    "babel-helper-function-name": "^6.23.0",
     "babel-plugin-syntax-class-properties": "^6.8.0",
-    "babel-template": "^6.22.0"
+    "babel-template": "^6.23.0"
   },
   "devDependencies": {
     "babel-helper-plugin-test-runner": "^6.22.0"
diff --git a/packages/babel-plugin-transform-es2015-block-scoping/package.json b/packages/babel-plugin-transform-es2015-block-scoping/package.json
index ef72fdfecf2b..569706fca18c 100644
--- a/packages/babel-plugin-transform-es2015-block-scoping/package.json
+++ b/packages/babel-plugin-transform-es2015-block-scoping/package.json
@@ -1,14 +1,14 @@
 {
   "name": "babel-plugin-transform-es2015-block-scoping",
-  "version": "6.22.0",
+  "version": "6.23.0",
   "description": "Compile ES2015 block scoping (const and let) to ES5",
   "repository": "https://github.com/babel/babel/tree/master/packages/babel-plugin-transform-es2015-block-scoping",
   "license": "MIT",
   "main": "lib/index.js",
   "dependencies": {
-    "babel-traverse": "^6.22.0",
-    "babel-types": "^6.22.0",
-    "babel-template": "^6.22.0",
+    "babel-traverse": "^6.23.0",
+    "babel-types": "^6.23.0",
+    "babel-template": "^6.23.0",
     "lodash": "^4.2.0"
   },
   "keywords": [
diff --git a/packages/babel-plugin-transform-es2015-block-scoping/src/index.js b/packages/babel-plugin-transform-es2015-block-scoping/src/index.js
index b1227d3a52c0..f63305462297 100644
--- a/packages/babel-plugin-transform-es2015-block-scoping/src/index.js
+++ b/packages/babel-plugin-transform-es2015-block-scoping/src/index.js
@@ -112,8 +112,21 @@ function isVar(node) {
 }
 
 const letReferenceBlockVisitor = traverse.visitors.merge([{
+  Loop: {
+    enter(path, state) {
+      state.loopDepth++;
+    },
+    exit(path, state) {
+      state.loopDepth--;
+    },
+  },
   Function(path, state) {
-    path.traverse(letReferenceFunctionVisitor, state);
+    // References to block-scoped variables only require added closures if it's
+    // possible for the code to run more than once -- otherwise it is safe to
+    // simply rename the variables.
+    if (state.loopDepth > 0) {
+      path.traverse(letReferenceFunctionVisitor, state);
+    }
     return path.skip();
   }
 }, tdzVisitor]);
@@ -549,9 +562,19 @@ class BlockScoping {
     const state = {
       letReferences: this.letReferences,
       closurify:     false,
-      file:          this.file
+      file:          this.file,
+      loopDepth:     0,
     };
 
+    const loopOrFunctionParent = this.blockPath.find(
+      (path) => path.isLoop() || path.isFunction()
+    );
+    if (loopOrFunctionParent && loopOrFunctionParent.isLoop()) {
+      // There is a loop ancestor closer than the closest function, so we
+      // consider ourselves to be in a loop.
+      state.loopDepth++;
+    }
+
     // traverse through this block, stopping on functions and checking if they
     // contain any local let references
     this.blockPath.traverse(letReferenceBlockVisitor, state);
diff --git a/packages/babel-plugin-transform-es2015-block-scoping/test/fixtures/general/issue-2174/expected.js b/packages/babel-plugin-transform-es2015-block-scoping/test/fixtures/general/issue-2174/expected.js
index 1dce9c4c174c..9efbc1091f2b 100644
--- a/packages/babel-plugin-transform-es2015-block-scoping/test/fixtures/general/issue-2174/expected.js
+++ b/packages/babel-plugin-transform-es2015-block-scoping/test/fixtures/general/issue-2174/expected.js
@@ -1,11 +1,9 @@
 if (true) {
-  var x;
+  var foo = function () {};
 
-  (function () {
-    function foo() {}
-    function bar() {
-      return foo;
-    }
-    for (x in {}) {}
-  })();
+  var bar = function () {
+    return foo;
+  };
+
+  for (var x in {}) {}
 }
diff --git a/packages/babel-plugin-transform-es2015-block-scoping/test/fixtures/general/loops-and-no-loops/actual.js b/packages/babel-plugin-transform-es2015-block-scoping/test/fixtures/general/loops-and-no-loops/actual.js
new file mode 100644
index 000000000000..f030ac811de4
--- /dev/null
+++ b/packages/babel-plugin-transform-es2015-block-scoping/test/fixtures/general/loops-and-no-loops/actual.js
@@ -0,0 +1,34 @@
+function foo() {
+  const x = 5;
+  console.log(x);
+
+  {
+    const x = 7;
+    setTimeout(() => x, 0);
+  }
+}
+
+function bar() {
+  const x = 5;
+  console.log(x);
+
+  for (let i = 0; i < 7; i++) {
+    {
+      const x = i;
+      setTimeout(() => x, 0);
+    }
+  }
+}
+
+function baz() {
+  const x = 5;
+  console.log(x);
+
+  for (let i = 0; i < 7; i++) {
+    var qux = function qux(y) {
+      const x = y;
+      setTimeout(() => x, 0);
+    };
+    qux(i);
+  }
+}
diff --git a/packages/babel-plugin-transform-es2015-block-scoping/test/fixtures/general/loops-and-no-loops/expected.js b/packages/babel-plugin-transform-es2015-block-scoping/test/fixtures/general/loops-and-no-loops/expected.js
new file mode 100644
index 000000000000..a86a2e481147
--- /dev/null
+++ b/packages/babel-plugin-transform-es2015-block-scoping/test/fixtures/general/loops-and-no-loops/expected.js
@@ -0,0 +1,42 @@
+function foo() {
+  var x = 5;
+  console.log(x);
+
+  {
+    var _x = 7;
+    setTimeout(function () {
+      return _x;
+    }, 0);
+  }
+}
+
+function bar() {
+  var x = 5;
+  console.log(x);
+
+  for (var i = 0; i < 7; i++) {
+    {
+      (function () {
+        var x = i;
+        setTimeout(function () {
+          return x;
+        }, 0);
+      })();
+    }
+  }
+}
+
+function baz() {
+  var x = 5;
+  console.log(x);
+
+  for (var i = 0; i < 7; i++) {
+    var qux = function qux(y) {
+      var x = y;
+      setTimeout(function () {
+        return x;
+      }, 0);
+    };
+    qux(i);
+  }
+}
diff --git a/packages/babel-plugin-transform-es2015-block-scoping/test/fixtures/general/sibling-scopes/actual.js b/packages/babel-plugin-transform-es2015-block-scoping/test/fixtures/general/sibling-scopes/actual.js
new file mode 100644
index 000000000000..e3020dada7f6
--- /dev/null
+++ b/packages/babel-plugin-transform-es2015-block-scoping/test/fixtures/general/sibling-scopes/actual.js
@@ -0,0 +1,11 @@
+var f1, f2;
+{
+  let z = 'z1 value';
+  f1 = function() { return z; };
+}
+{
+  let z = 'z2 value';
+  f2 = function() { return z; };
+}
+f1();
+f2();
diff --git a/packages/babel-plugin-transform-es2015-block-scoping/test/fixtures/general/sibling-scopes/expected.js b/packages/babel-plugin-transform-es2015-block-scoping/test/fixtures/general/sibling-scopes/expected.js
new file mode 100644
index 000000000000..8bbdfc7ddff4
--- /dev/null
+++ b/packages/babel-plugin-transform-es2015-block-scoping/test/fixtures/general/sibling-scopes/expected.js
@@ -0,0 +1,15 @@
+var f1, f2;
+{
+  var z = 'z1 value';
+  f1 = function () {
+    return z;
+  };
+}
+{
+  var _z = 'z2 value';
+  f2 = function () {
+    return _z;
+  };
+}
+f1();
+f2();
\ No newline at end of file
diff --git a/packages/babel-plugin-transform-es2015-block-scoping/test/fixtures/general/superswitch/actual.js b/packages/babel-plugin-transform-es2015-block-scoping/test/fixtures/general/superswitch/actual.js
index 857b8641f415..5dedf9a59244 100644
--- a/packages/babel-plugin-transform-es2015-block-scoping/test/fixtures/general/superswitch/actual.js
+++ b/packages/babel-plugin-transform-es2015-block-scoping/test/fixtures/general/superswitch/actual.js
@@ -1,16 +1,18 @@
 function foo() {
-  switch (2) {
-    case 0: {
-      if (true) {
-        return;
-      }
+  while (true) {
+    switch (2) {
+      case 0: {
+        if (true) {
+          return;
+        }
 
-      const stuff = new Map();
-      const data = 0;
-      stuff.forEach(() => {
-        const d = data;
-      });
-      break;
+        const stuff = new Map();
+        const data = 0;
+        stuff.forEach(() => {
+          const d = data;
+        });
+        break;
+      }
     }
   }
 }
diff --git a/packages/babel-plugin-transform-es2015-block-scoping/test/fixtures/general/superswitch/expected.js b/packages/babel-plugin-transform-es2015-block-scoping/test/fixtures/general/superswitch/expected.js
index 05d7afe3d96c..80b21eba9cdc 100644
--- a/packages/babel-plugin-transform-es2015-block-scoping/test/fixtures/general/superswitch/expected.js
+++ b/packages/babel-plugin-transform-es2015-block-scoping/test/fixtures/general/superswitch/expected.js
@@ -1,29 +1,31 @@
 function foo() {
-  switch (2) {
-    case 0:
-      {
-        var _ret = function () {
-          if (true) {
-            return {
-              v: void 0
-            };
-          }
+  while (true) {
+    switch (2) {
+      case 0:
+        {
+          var _ret = function () {
+            if (true) {
+              return {
+                v: void 0
+              };
+            }
 
-          var stuff = new Map();
-          var data = 0;
-          stuff.forEach(function () {
-            var d = data;
-          });
-          return "break";
-        }();
+            var stuff = new Map();
+            var data = 0;
+            stuff.forEach(function () {
+              var d = data;
+            });
+            return "break";
+          }();
 
-        switch (_ret) {
-          case "break":
-            break;
+          switch (_ret) {
+            case "break":
+              break;
 
-          default:
-            if (typeof _ret === "object") return _ret.v;
+            default:
+              if (typeof _ret === "object") return _ret.v;
+          }
         }
-      }
+    }
   }
 }
diff --git a/packages/babel-plugin-transform-es2015-block-scoping/test/fixtures/general/switch-callbacks/actual.js b/packages/babel-plugin-transform-es2015-block-scoping/test/fixtures/general/switch-callbacks/actual.js
index c57bdc6e5150..99f8726f058a 100644
--- a/packages/babel-plugin-transform-es2015-block-scoping/test/fixtures/general/switch-callbacks/actual.js
+++ b/packages/babel-plugin-transform-es2015-block-scoping/test/fixtures/general/switch-callbacks/actual.js
@@ -1,10 +1,12 @@
 function fn() {
-    switch (true) {
-    default:
-        let foo = 4;
-        if (true) {
-            let bar = () => foo;
-            console.log(bar());
+    while (true) {
+        switch (true) {
+        default:
+            let foo = 4;
+            if (true) {
+                let bar = () => foo;
+                console.log(bar());
+            }
         }
     }
 }
diff --git a/packages/babel-plugin-transform-es2015-block-scoping/test/fixtures/general/switch-callbacks/expected.js b/packages/babel-plugin-transform-es2015-block-scoping/test/fixtures/general/switch-callbacks/expected.js
index 2efd145af333..40f23daea608 100644
--- a/packages/babel-plugin-transform-es2015-block-scoping/test/fixtures/general/switch-callbacks/expected.js
+++ b/packages/babel-plugin-transform-es2015-block-scoping/test/fixtures/general/switch-callbacks/expected.js
@@ -1,14 +1,16 @@
 function fn() {
-    (function () {
-        switch (true) {
-            default:
-                var foo = 4;
-                if (true) {
-                    var bar = function () {
-                        return foo;
-                    };
-                    console.log(bar());
-                }
-        }
-    })();
+    while (true) {
+        (function () {
+            switch (true) {
+                default:
+                    var foo = 4;
+                    if (true) {
+                        var bar = function () {
+                            return foo;
+                        };
+                        console.log(bar());
+                    }
+            }
+        })();
+    }
 }
diff --git a/packages/babel-plugin-transform-es2015-block-scoping/test/fixtures/throwIfClosureRequired/for-const-closure/expected.js b/packages/babel-plugin-transform-es2015-block-scoping/test/fixtures/throwIfClosureRequired/for-const-closure/expected.js
new file mode 100644
index 000000000000..c28cb3bf748e
--- /dev/null
+++ b/packages/babel-plugin-transform-es2015-block-scoping/test/fixtures/throwIfClosureRequired/for-const-closure/expected.js
@@ -0,0 +1,6 @@
+for (var i = 0; i < 5; i++) {
+  var l = i;
+  setTimeout(function () {
+    console.log(l);
+  }, 1);
+}
\ No newline at end of file
diff --git a/packages/babel-plugin-transform-es2015-block-scoping/test/fixtures/throwIfClosureRequired/superswitch/actual.js b/packages/babel-plugin-transform-es2015-block-scoping/test/fixtures/throwIfClosureRequired/superswitch/actual.js
deleted file mode 100644
index 857b8641f415..000000000000
--- a/packages/babel-plugin-transform-es2015-block-scoping/test/fixtures/throwIfClosureRequired/superswitch/actual.js
+++ /dev/null
@@ -1,16 +0,0 @@
-function foo() {
-  switch (2) {
-    case 0: {
-      if (true) {
-        return;
-      }
-
-      const stuff = new Map();
-      const data = 0;
-      stuff.forEach(() => {
-        const d = data;
-      });
-      break;
-    }
-  }
-}
diff --git a/packages/babel-plugin-transform-es2015-block-scoping/test/fixtures/throwIfClosureRequired/superswitch/options.json b/packages/babel-plugin-transform-es2015-block-scoping/test/fixtures/throwIfClosureRequired/superswitch/options.json
deleted file mode 100644
index d210fdebfc97..000000000000
--- a/packages/babel-plugin-transform-es2015-block-scoping/test/fixtures/throwIfClosureRequired/superswitch/options.json
+++ /dev/null
@@ -1,3 +0,0 @@
-{
-  "throws": "Compiling let/const in this block would add a closure (throwIfClosureRequired)."
-}
diff --git a/packages/babel-plugin-transform-es2015-classes/package.json b/packages/babel-plugin-transform-es2015-classes/package.json
index 1d17d0b74835..cd552e395d28 100644
--- a/packages/babel-plugin-transform-es2015-classes/package.json
+++ b/packages/babel-plugin-transform-es2015-classes/package.json
@@ -1,19 +1,19 @@
 {
   "name": "babel-plugin-transform-es2015-classes",
-  "version": "6.22.0",
+  "version": "6.23.0",
   "description": "Compile ES2015 classes to ES5",
   "repository": "https://github.com/babel/babel/tree/master/packages/babel-plugin-transform-es2015-classes",
   "license": "MIT",
   "main": "lib/index.js",
   "dependencies": {
-    "babel-helper-optimise-call-expression": "^6.22.0",
-    "babel-helper-function-name": "^6.22.0",
-    "babel-helper-replace-supers": "^6.22.0",
-    "babel-template": "^6.22.0",
-    "babel-traverse": "^6.22.0",
-    "babel-helper-define-map": "^6.22.0",
-    "babel-messages": "^6.22.0",
-    "babel-types": "^6.22.0"
+    "babel-helper-optimise-call-expression": "^6.23.0",
+    "babel-helper-function-name": "^6.23.0",
+    "babel-helper-replace-supers": "^6.23.0",
+    "babel-template": "^6.23.0",
+    "babel-traverse": "^6.23.0",
+    "babel-helper-define-map": "^6.23.0",
+    "babel-messages": "^6.23.0",
+    "babel-types": "^6.23.0"
   },
   "keywords": [
     "babel-plugin"
diff --git a/packages/babel-plugin-transform-es2015-destructuring/package.json b/packages/babel-plugin-transform-es2015-destructuring/package.json
index 4eb5eb75aee5..53b5174965fd 100644
--- a/packages/babel-plugin-transform-es2015-destructuring/package.json
+++ b/packages/babel-plugin-transform-es2015-destructuring/package.json
@@ -1,6 +1,6 @@
 {
   "name": "babel-plugin-transform-es2015-destructuring",
-  "version": "6.22.0",
+  "version": "6.23.0",
   "description": "Compile ES2015 destructuring to ES5",
   "repository": "https://github.com/babel/babel/tree/master/packages/babel-plugin-transform-es2015-destructuring",
   "license": "MIT",
diff --git a/packages/babel-plugin-transform-es2015-for-of/package.json b/packages/babel-plugin-transform-es2015-for-of/package.json
index 53b2959969f4..99c92140bf8f 100644
--- a/packages/babel-plugin-transform-es2015-for-of/package.json
+++ b/packages/babel-plugin-transform-es2015-for-of/package.json
@@ -1,6 +1,6 @@
 {
   "name": "babel-plugin-transform-es2015-for-of",
-  "version": "6.22.0",
+  "version": "6.23.0",
   "description": "Compile ES2015 for...of to ES5",
   "repository": "https://github.com/babel/babel/tree/master/packages/babel-plugin-transform-es2015-for-of",
   "license": "MIT",
diff --git a/packages/babel-plugin-transform-es2015-for-of/src/index.js b/packages/babel-plugin-transform-es2015-for-of/src/index.js
index 958eae6bce1b..b0b3a6bcbffc 100644
--- a/packages/babel-plugin-transform-es2015-for-of/src/index.js
+++ b/packages/babel-plugin-transform-es2015-for-of/src/index.js
@@ -135,9 +135,8 @@ export default function ({ messages, template, types: t }) {
   };
 
   function loose(path, file) {
-    const { node, scope } = path;
-
-    const left = node.left;
+    const { node, scope, parent } = path;
+    const { left } = node;
     let declar, id;
 
     if (t.isIdentifier(left) || t.isPattern(left) || t.isMemberExpression(left)) {
@@ -171,11 +170,18 @@ export default function ({ messages, template, types: t }) {
     }
 
     //
+    const isLabeledParent = t.isLabeledStatement(parent);
+    let labeled;
+
+    if (isLabeledParent) {
+      labeled = t.labeledStatement(parent.label, loop);
+    }
 
     return {
-      declar: declar,
-      node:   loop,
-      loop:   loop
+      replaceParent: isLabeledParent,
+      declar:        declar,
+      node:          labeled || loop,
+      loop:          loop
     };
   }
 
diff --git a/packages/babel-plugin-transform-es2015-for-of/test/fixtures/loose/nested-label-for-of/actual.js b/packages/babel-plugin-transform-es2015-for-of/test/fixtures/loose/nested-label-for-of/actual.js
new file mode 100644
index 000000000000..73c8203449d4
--- /dev/null
+++ b/packages/babel-plugin-transform-es2015-for-of/test/fixtures/loose/nested-label-for-of/actual.js
@@ -0,0 +1,5 @@
+b: for (let c of d()) {
+  for (let e of f()) {
+    continue b;
+  }
+}
diff --git a/packages/babel-plugin-transform-es2015-for-of/test/fixtures/loose/nested-label-for-of/expected.js b/packages/babel-plugin-transform-es2015-for-of/test/fixtures/loose/nested-label-for-of/expected.js
new file mode 100644
index 000000000000..e3e9396649ef
--- /dev/null
+++ b/packages/babel-plugin-transform-es2015-for-of/test/fixtures/loose/nested-label-for-of/expected.js
@@ -0,0 +1,31 @@
+b: for (var _iterator = d(), _isArray = Array.isArray(_iterator), _i = 0, _iterator = _isArray ? _iterator : _iterator[Symbol.iterator]();;) {
+  var _ref;
+
+  if (_isArray) {
+    if (_i >= _iterator.length) break;
+    _ref = _iterator[_i++];
+  } else {
+    _i = _iterator.next();
+    if (_i.done) break;
+    _ref = _i.value;
+  }
+
+  let c = _ref;
+
+  for (var _iterator2 = f(), _isArray2 = Array.isArray(_iterator2), _i2 = 0, _iterator2 = _isArray2 ? _iterator2 : _iterator2[Symbol.iterator]();;) {
+    var _ref2;
+
+    if (_isArray2) {
+      if (_i2 >= _iterator2.length) break;
+      _ref2 = _iterator2[_i2++];
+    } else {
+      _i2 = _iterator2.next();
+      if (_i2.done) break;
+      _ref2 = _i2.value;
+    }
+
+    let e = _ref2;
+
+    continue b;
+  }
+}
diff --git a/packages/babel-plugin-transform-es2015-modules-commonjs/package.json b/packages/babel-plugin-transform-es2015-modules-commonjs/package.json
index 923bf06419bf..47cca38a41d6 100644
--- a/packages/babel-plugin-transform-es2015-modules-commonjs/package.json
+++ b/packages/babel-plugin-transform-es2015-modules-commonjs/package.json
@@ -1,13 +1,13 @@
 {
   "name": "babel-plugin-transform-es2015-modules-commonjs",
-  "version": "6.22.0",
+  "version": "6.23.0",
   "description": "This plugin transforms ES2015 modules to CommonJS",
   "repository": "https://github.com/babel/babel/tree/master/packages/babel-plugin-transform-es2015-modules-commonjs",
   "license": "MIT",
   "main": "lib/index.js",
   "dependencies": {
-    "babel-types": "^6.22.0",
-    "babel-template": "^6.22.0",
+    "babel-types": "^6.23.0",
+    "babel-template": "^6.23.0",
     "babel-plugin-transform-strict-mode": "^6.22.0"
   },
   "keywords": [
diff --git a/packages/babel-plugin-transform-es2015-modules-systemjs/package.json b/packages/babel-plugin-transform-es2015-modules-systemjs/package.json
index 73cdf2d9c589..4d6e0841fbe0 100644
--- a/packages/babel-plugin-transform-es2015-modules-systemjs/package.json
+++ b/packages/babel-plugin-transform-es2015-modules-systemjs/package.json
@@ -1,12 +1,12 @@
 {
   "name": "babel-plugin-transform-es2015-modules-systemjs",
-  "version": "6.22.0",
+  "version": "6.23.0",
   "description": "This plugin transforms ES2015 modules to SystemJS",
   "repository": "https://github.com/babel/babel/tree/master/packages/babel-plugin-transform-es2015-modules-systemjs",
   "license": "MIT",
   "main": "lib/index.js",
   "dependencies": {
-    "babel-template": "^6.22.0",
+    "babel-template": "^6.23.0",
     "babel-helper-hoist-variables": "^6.22.0"
   },
   "keywords": [
diff --git a/packages/babel-plugin-transform-es2015-modules-umd/package.json b/packages/babel-plugin-transform-es2015-modules-umd/package.json
index 95944f163b55..d4a5a0e71d8b 100644
--- a/packages/babel-plugin-transform-es2015-modules-umd/package.json
+++ b/packages/babel-plugin-transform-es2015-modules-umd/package.json
@@ -1,13 +1,13 @@
 {
   "name": "babel-plugin-transform-es2015-modules-umd",
-  "version": "6.22.0",
+  "version": "6.23.0",
   "description": "This plugin transforms ES2015 modules to UMD",
   "repository": "https://github.com/babel/babel/tree/master/packages/babel-plugin-transform-es2015-modules-umd",
   "license": "MIT",
   "main": "lib/index.js",
   "dependencies": {
     "babel-plugin-transform-es2015-modules-amd": "^6.22.0",
-    "babel-template": "^6.22.0"
+    "babel-template": "^6.23.0"
   },
   "keywords": [
     "babel-plugin"
diff --git a/packages/babel-plugin-transform-es2015-parameters/package.json b/packages/babel-plugin-transform-es2015-parameters/package.json
index 72fdeee2a421..1dec6ec1515d 100644
--- a/packages/babel-plugin-transform-es2015-parameters/package.json
+++ b/packages/babel-plugin-transform-es2015-parameters/package.json
@@ -1,16 +1,16 @@
 {
   "name": "babel-plugin-transform-es2015-parameters",
-  "version": "6.22.0",
+  "version": "6.23.0",
   "description": "Compile ES2015 default and rest parameters to ES5",
   "repository": "https://github.com/babel/babel/tree/master/packages/babel-plugin-transform-es2015-parameters",
   "license": "MIT",
   "main": "lib/index.js",
   "dependencies": {
-    "babel-traverse": "^6.22.0",
+    "babel-traverse": "^6.23.0",
     "babel-helper-call-delegate": "^6.22.0",
     "babel-helper-get-function-arity": "^6.22.0",
-    "babel-template": "^6.22.0",
-    "babel-types": "^6.22.0"
+    "babel-template": "^6.23.0",
+    "babel-types": "^6.23.0"
   },
   "keywords": [
     "babel-plugin"
diff --git a/packages/babel-plugin-transform-es2015-typeof-symbol/package.json b/packages/babel-plugin-transform-es2015-typeof-symbol/package.json
index 323c189e9345..75fb73930ea1 100644
--- a/packages/babel-plugin-transform-es2015-typeof-symbol/package.json
+++ b/packages/babel-plugin-transform-es2015-typeof-symbol/package.json
@@ -1,6 +1,6 @@
 {
   "name": "babel-plugin-transform-es2015-typeof-symbol",
-  "version": "6.22.0",
+  "version": "6.23.0",
   "description": "This transformer wraps all typeof expressions with a method that replicates native behaviour. (ie. returning “symbol” for symbols)",
   "repository": "https://github.com/babel/babel/tree/master/packages/babel-plugin-transform-es2015-typeof-symbol",
   "license": "MIT",
diff --git a/packages/babel-plugin-transform-object-rest-spread/package.json b/packages/babel-plugin-transform-object-rest-spread/package.json
index b3686266c18a..d4bdce78b56a 100644
--- a/packages/babel-plugin-transform-object-rest-spread/package.json
+++ b/packages/babel-plugin-transform-object-rest-spread/package.json
@@ -1,6 +1,6 @@
 {
   "name": "babel-plugin-transform-object-rest-spread",
-  "version": "6.22.0",
+  "version": "6.23.0",
   "description": "Compile object rest and spread to ES5",
   "repository": "https://github.com/babel/babel/tree/master/packages/babel-plugin-transform-object-rest-spread",
   "license": "MIT",
diff --git a/packages/babel-plugin-transform-proto-to-assign/package.json b/packages/babel-plugin-transform-proto-to-assign/package.json
index b0eb2e46e11c..8817ae36f6e4 100644
--- a/packages/babel-plugin-transform-proto-to-assign/package.json
+++ b/packages/babel-plugin-transform-proto-to-assign/package.json
@@ -1,6 +1,6 @@
 {
   "name": "babel-plugin-transform-proto-to-assign",
-  "version": "6.22.0",
+  "version": "6.23.0",
   "description": "Babel plugin for turning __proto__ into a shallow property clone",
   "repository": "https://github.com/babel/babel/tree/master/packages/babel-plugin-transform-proto-to-assign",
   "license": "MIT",
diff --git a/packages/babel-plugin-transform-react-constant-elements/package.json b/packages/babel-plugin-transform-react-constant-elements/package.json
index 79d30ac76273..77c911d9a775 100644
--- a/packages/babel-plugin-transform-react-constant-elements/package.json
+++ b/packages/babel-plugin-transform-react-constant-elements/package.json
@@ -1,6 +1,6 @@
 {
   "name": "babel-plugin-transform-react-constant-elements",
-  "version": "6.22.0",
+  "version": "6.23.0",
   "description": "Treat React JSX elements as value types and hoist them to the highest scope",
   "repository": "https://github.com/babel/babel/tree/master/packages/babel-plugin-transform-react-constant-elements",
   "license": "MIT",
diff --git a/packages/babel-plugin-transform-react-constant-elements/src/index.js b/packages/babel-plugin-transform-react-constant-elements/src/index.js
index a25fb67e6c6d..b38f2008d154 100644
--- a/packages/babel-plugin-transform-react-constant-elements/src/index.js
+++ b/packages/babel-plugin-transform-react-constant-elements/src/index.js
@@ -1,4 +1,4 @@
-export default function () {
+export default function ({ types: t }) {
   const immutabilityVisitor = {
     enter(path, state) {
       const stop = () => {
@@ -11,15 +11,39 @@ export default function () {
         return;
       }
 
+      // Elements with refs are not safe to hoist.
       if (path.isJSXIdentifier({ name: "ref" }) && path.parentPath.isJSXAttribute({ name: path.node })) {
         return stop();
       }
 
+      // Ignore identifiers & JSX expressions.
       if (path.isJSXIdentifier() || path.isIdentifier() || path.isJSXMemberExpression()) {
         return;
       }
 
-      if (!path.isImmutable()) stop();
+      if (!path.isImmutable()) {
+        // If it's not immutable, it may still be a pure expression, such as string concatenation.
+        // It is still safe to hoist that, so long as its result is immutable.
+        // If not, it is not safe to replace as mutable values (like objects) could be mutated after render.
+        // https://github.com/facebook/react/issues/3226
+        if (path.isPure()) {
+          const expressionResult = path.evaluate();
+          if (expressionResult.confident) {
+            // We know the result; check its mutability.
+            const { value } = expressionResult;
+            const isMutable = (value && typeof value === "object") || (typeof value === "function");
+            if (!isMutable) {
+              // It evaluated to an immutable value, so we can hoist it.
+              return;
+            }
+          } else if (t.isIdentifier(expressionResult.deopt)) {
+            // It's safe to hoist here if the deopt reason is an identifier (e.g. func param).
+            // The hoister will take care of how high up it can be hoisted.
+            return;
+          }
+        }
+        stop();
+      }
     }
   };
 
diff --git a/packages/babel-plugin-transform-react-constant-elements/test/fixtures/constant-elements/append-to-end-when-declared-in-scope-3/expected.js b/packages/babel-plugin-transform-react-constant-elements/test/fixtures/constant-elements/append-to-end-when-declared-in-scope-3/expected.js
index cceca3a5e883..46849febf69f 100644
--- a/packages/babel-plugin-transform-react-constant-elements/test/fixtures/constant-elements/append-to-end-when-declared-in-scope-3/expected.js
+++ b/packages/babel-plugin-transform-react-constant-elements/test/fixtures/constant-elements/append-to-end-when-declared-in-scope-3/expected.js
@@ -1,18 +1,19 @@
-var _ref = <p>Parent</p>;
-
 var _ref2 = <div>child</div>;
 
+var _ref3 = <p>Parent</p>;
+
 (function () {
   class App extends React.Component {
     render() {
-      return <div>
-          {_ref}
-          <AppItem />
-        </div>;
+      return _ref;
     }
   }
 
   const AppItem = () => {
     return _ref2;
-  };
-});
+  },
+        _ref = <div>
+          {_ref3}
+          <AppItem />
+        </div>;
+});
\ No newline at end of file
diff --git a/packages/babel-plugin-transform-react-constant-elements/test/fixtures/constant-elements/append-to-end-when-declared-in-scope/expected.js b/packages/babel-plugin-transform-react-constant-elements/test/fixtures/constant-elements/append-to-end-when-declared-in-scope/expected.js
index 5fc826084567..fe04d4853fea 100644
--- a/packages/babel-plugin-transform-react-constant-elements/test/fixtures/constant-elements/append-to-end-when-declared-in-scope/expected.js
+++ b/packages/babel-plugin-transform-react-constant-elements/test/fixtures/constant-elements/append-to-end-when-declared-in-scope/expected.js
@@ -1,16 +1,14 @@
-var _ref = <p>Parent</p>;
-
 export default class App extends React.Component {
   render() {
-    return <div>
-        {_ref}
-        <AppItem />
-      </div>;
+    return _ref;
   }
 }
 
-var _ref2 = <div>child</div>;
-
-const AppItem = () => {
+const _ref2 = <div>child</div>,
+      AppItem = () => {
   return _ref2;
-};
+},
+      _ref = <div>
+        <p>Parent</p>
+        <AppItem />
+      </div>;
\ No newline at end of file
diff --git a/packages/babel-plugin-transform-react-constant-elements/test/fixtures/constant-elements/dont-hoist-before-class/actual.js b/packages/babel-plugin-transform-react-constant-elements/test/fixtures/constant-elements/dont-hoist-before-class/actual.js
new file mode 100644
index 000000000000..0bcdd9ef7c39
--- /dev/null
+++ b/packages/babel-plugin-transform-react-constant-elements/test/fixtures/constant-elements/dont-hoist-before-class/actual.js
@@ -0,0 +1,15 @@
+import React from "react";
+
+const Parent = ({}) => (
+  <div className="parent">
+    <Child/>
+  </div>
+);
+
+export default Parent;
+
+let Child = () => (
+  <div className="child">
+    ChildTextContent
+  </div>
+);
diff --git a/packages/babel-plugin-transform-react-constant-elements/test/fixtures/constant-elements/dont-hoist-before-class/expected.js b/packages/babel-plugin-transform-react-constant-elements/test/fixtures/constant-elements/dont-hoist-before-class/expected.js
new file mode 100644
index 000000000000..6bcd6e0ffbd8
--- /dev/null
+++ b/packages/babel-plugin-transform-react-constant-elements/test/fixtures/constant-elements/dont-hoist-before-class/expected.js
@@ -0,0 +1,13 @@
+import React from "react";
+
+const Parent = ({}) => _ref;
+
+export default Parent;
+
+let _ref2 = <div className="child">
+    ChildTextContent
+  </div>,
+    Child = () => _ref2,
+    _ref = <div className="parent">
+    <Child />
+  </div>;
diff --git a/packages/babel-plugin-transform-react-constant-elements/test/fixtures/constant-elements/dont-hoist-before-declaration/expected.js b/packages/babel-plugin-transform-react-constant-elements/test/fixtures/constant-elements/dont-hoist-before-declaration/expected.js
index d85f9f3244c6..45b91bd2961c 100644
--- a/packages/babel-plugin-transform-react-constant-elements/test/fixtures/constant-elements/dont-hoist-before-declaration/expected.js
+++ b/packages/babel-plugin-transform-react-constant-elements/test/fixtures/constant-elements/dont-hoist-before-declaration/expected.js
@@ -8,8 +8,9 @@ function render() {
 
 function render() {
   const bar = "bar",
-        renderFoo = () => <foo bar={bar} baz={baz} />,
-        baz = "baz";
+        renderFoo = () => _ref2,
+        baz = "baz",
+        _ref2 = <foo bar={bar} baz={baz} />;
 
   return renderFoo();
 }
\ No newline at end of file
diff --git a/packages/babel-plugin-transform-react-constant-elements/test/fixtures/constant-elements/dont-hoist-before-hoc/actual.js b/packages/babel-plugin-transform-react-constant-elements/test/fixtures/constant-elements/dont-hoist-before-hoc/actual.js
new file mode 100644
index 000000000000..21f7b2ed905d
--- /dev/null
+++ b/packages/babel-plugin-transform-react-constant-elements/test/fixtures/constant-elements/dont-hoist-before-hoc/actual.js
@@ -0,0 +1,18 @@
+import React from "react";
+
+const HOC = component => component;
+
+const Parent = ({}) => (
+  <div className="parent">
+    <Child/>
+  </div>
+);
+
+export default Parent;
+
+let Child = () => (
+  <div className="child">
+    ChildTextContent
+  </div>
+);
+Child = HOC(Child);
diff --git a/packages/babel-plugin-transform-react-constant-elements/test/fixtures/constant-elements/dont-hoist-before-hoc/expected.js b/packages/babel-plugin-transform-react-constant-elements/test/fixtures/constant-elements/dont-hoist-before-hoc/expected.js
new file mode 100644
index 000000000000..8da0cc5ad12f
--- /dev/null
+++ b/packages/babel-plugin-transform-react-constant-elements/test/fixtures/constant-elements/dont-hoist-before-hoc/expected.js
@@ -0,0 +1,18 @@
+import React from "react";
+
+const HOC = component => component;
+
+const Parent = ({}) => _ref;
+
+export default Parent;
+
+var _ref2 = <div className="child">
+    ChildTextContent
+  </div>;
+
+let Child = () => _ref2;
+Child = HOC(Child);
+
+var _ref = <div className="parent">
+    <Child />
+  </div>;
\ No newline at end of file
diff --git a/packages/babel-plugin-transform-react-constant-elements/test/fixtures/constant-elements/dont-hoist-block-scoped-variables/expected.js b/packages/babel-plugin-transform-react-constant-elements/test/fixtures/constant-elements/dont-hoist-block-scoped-variables/expected.js
index 9618e6da028f..ab6ad7d4c478 100644
--- a/packages/babel-plugin-transform-react-constant-elements/test/fixtures/constant-elements/dont-hoist-block-scoped-variables/expected.js
+++ b/packages/babel-plugin-transform-react-constant-elements/test/fixtures/constant-elements/dont-hoist-block-scoped-variables/expected.js
@@ -1,17 +1,11 @@
 function render(flag) {
   if (flag) {
-    var _ret = function () {
-      var bar = "bar";
+    var bar = "bar";
 
-      [].map(() => bar);
+    [].map(() => bar);
 
-      return {
-        v: <foo bar={bar} />
-      };
-    }();
-
-    if (typeof _ret === "object") return _ret.v;
+    return <foo bar={bar} />;
   }
 
   return null;
-}
\ No newline at end of file
+}
diff --git a/packages/babel-plugin-transform-react-constant-elements/test/fixtures/constant-elements/member-expression-constant/actual.js b/packages/babel-plugin-transform-react-constant-elements/test/fixtures/constant-elements/member-expression-constant/actual.js
new file mode 100644
index 000000000000..a6c1f9b6ec88
--- /dev/null
+++ b/packages/babel-plugin-transform-react-constant-elements/test/fixtures/constant-elements/member-expression-constant/actual.js
@@ -0,0 +1,4 @@
+function render() {
+  this.component = "div";
+  return () => <this.component />;
+}
diff --git a/packages/babel-plugin-transform-react-constant-elements/test/fixtures/constant-elements/member-expression-constant/expected.js b/packages/babel-plugin-transform-react-constant-elements/test/fixtures/constant-elements/member-expression-constant/expected.js
new file mode 100644
index 000000000000..aa7a9994baeb
--- /dev/null
+++ b/packages/babel-plugin-transform-react-constant-elements/test/fixtures/constant-elements/member-expression-constant/expected.js
@@ -0,0 +1,7 @@
+function render() {
+  this.component = "div";
+
+  var _ref = <this.component />;
+
+  return () => _ref;
+}
diff --git a/packages/babel-plugin-transform-react-constant-elements/test/fixtures/constant-elements/member-expression-this/actual.js b/packages/babel-plugin-transform-react-constant-elements/test/fixtures/constant-elements/member-expression-this/actual.js
new file mode 100644
index 000000000000..bdc61d684a69
--- /dev/null
+++ b/packages/babel-plugin-transform-react-constant-elements/test/fixtures/constant-elements/member-expression-this/actual.js
@@ -0,0 +1,5 @@
+class Component extends React.Component {
+  subComponent = () => <span>Sub Component</span>
+
+  render = () => <this.subComponent />
+}
diff --git a/packages/babel-plugin-transform-react-constant-elements/test/fixtures/constant-elements/member-expression-this/expected.js b/packages/babel-plugin-transform-react-constant-elements/test/fixtures/constant-elements/member-expression-this/expected.js
new file mode 100644
index 000000000000..9ce3a08e7437
--- /dev/null
+++ b/packages/babel-plugin-transform-react-constant-elements/test/fixtures/constant-elements/member-expression-this/expected.js
@@ -0,0 +1,12 @@
+var _ref = <span>Sub Component</span>;
+
+class Component extends React.Component {
+  constructor(...args) {
+    var _temp;
+
+    var _ref2 = <this.subComponent />;
+
+    return _temp = super(...args), this.subComponent = () => _ref, this.render = () => _ref2, _temp;
+  }
+
+}
diff --git a/packages/babel-plugin-transform-react-constant-elements/test/fixtures/constant-elements/member-expression-this/options.json b/packages/babel-plugin-transform-react-constant-elements/test/fixtures/constant-elements/member-expression-this/options.json
new file mode 100644
index 000000000000..d4789bbda3fb
--- /dev/null
+++ b/packages/babel-plugin-transform-react-constant-elements/test/fixtures/constant-elements/member-expression-this/options.json
@@ -0,0 +1,3 @@
+{
+  "plugins": ["syntax-jsx", "transform-react-constant-elements", "transform-class-properties"]
+}
diff --git a/packages/babel-plugin-transform-react-constant-elements/test/fixtures/constant-elements/member-expression/actual.js b/packages/babel-plugin-transform-react-constant-elements/test/fixtures/constant-elements/member-expression/actual.js
new file mode 100644
index 000000000000..2ab59df97b89
--- /dev/null
+++ b/packages/babel-plugin-transform-react-constant-elements/test/fixtures/constant-elements/member-expression/actual.js
@@ -0,0 +1,6 @@
+const els = {
+  subComponent: () => <span>Sub Component</span>
+};
+class Component extends React.Component {
+  render = () => <els.subComponent />
+}
diff --git a/packages/babel-plugin-transform-react-constant-elements/test/fixtures/constant-elements/member-expression/expected.js b/packages/babel-plugin-transform-react-constant-elements/test/fixtures/constant-elements/member-expression/expected.js
new file mode 100644
index 000000000000..fe12eb988d5d
--- /dev/null
+++ b/packages/babel-plugin-transform-react-constant-elements/test/fixtures/constant-elements/member-expression/expected.js
@@ -0,0 +1,16 @@
+var _ref = <span>Sub Component</span>;
+
+const els = {
+  subComponent: () => _ref
+};
+
+var _ref2 = <els.subComponent />;
+
+class Component extends React.Component {
+  constructor(...args) {
+    var _temp;
+
+    return _temp = super(...args), this.render = () => _ref2, _temp;
+  }
+
+}
diff --git a/packages/babel-plugin-transform-react-constant-elements/test/fixtures/constant-elements/member-expression/options.json b/packages/babel-plugin-transform-react-constant-elements/test/fixtures/constant-elements/member-expression/options.json
new file mode 100644
index 000000000000..d4789bbda3fb
--- /dev/null
+++ b/packages/babel-plugin-transform-react-constant-elements/test/fixtures/constant-elements/member-expression/options.json
@@ -0,0 +1,3 @@
+{
+  "plugins": ["syntax-jsx", "transform-react-constant-elements", "transform-class-properties"]
+}
diff --git a/packages/babel-plugin-transform-react-constant-elements/test/fixtures/constant-elements/pure-deopt/actual.js b/packages/babel-plugin-transform-react-constant-elements/test/fixtures/constant-elements/pure-deopt/actual.js
new file mode 100644
index 000000000000..4df51832c7ce
--- /dev/null
+++ b/packages/babel-plugin-transform-react-constant-elements/test/fixtures/constant-elements/pure-deopt/actual.js
@@ -0,0 +1,5 @@
+// https://github.com/facebook/react/issues/3226
+// Not safe to reuse because it is mutable
+function render() {
+  return <div style={{ width: 100 }} />;
+}
diff --git a/packages/babel-plugin-transform-react-constant-elements/test/fixtures/constant-elements/pure-deopt/expected.js b/packages/babel-plugin-transform-react-constant-elements/test/fixtures/constant-elements/pure-deopt/expected.js
new file mode 100644
index 000000000000..4df51832c7ce
--- /dev/null
+++ b/packages/babel-plugin-transform-react-constant-elements/test/fixtures/constant-elements/pure-deopt/expected.js
@@ -0,0 +1,5 @@
+// https://github.com/facebook/react/issues/3226
+// Not safe to reuse because it is mutable
+function render() {
+  return <div style={{ width: 100 }} />;
+}
diff --git a/packages/babel-plugin-transform-react-constant-elements/test/fixtures/constant-elements/pure-expression-2/actual.js b/packages/babel-plugin-transform-react-constant-elements/test/fixtures/constant-elements/pure-expression-2/actual.js
new file mode 100644
index 000000000000..0acb75cfaf6a
--- /dev/null
+++ b/packages/babel-plugin-transform-react-constant-elements/test/fixtures/constant-elements/pure-expression-2/actual.js
@@ -0,0 +1,5 @@
+function render(offset) {
+  return function () {
+    return <div tabIndex={offset + 1} />;
+  };
+}
diff --git a/packages/babel-plugin-transform-react-constant-elements/test/fixtures/constant-elements/pure-expression-2/expected.js b/packages/babel-plugin-transform-react-constant-elements/test/fixtures/constant-elements/pure-expression-2/expected.js
new file mode 100644
index 000000000000..65df627806b2
--- /dev/null
+++ b/packages/babel-plugin-transform-react-constant-elements/test/fixtures/constant-elements/pure-expression-2/expected.js
@@ -0,0 +1,8 @@
+function render(offset) {
+  var _ref = <div tabIndex={offset + 1} />;
+
+  return function () {
+    return _ref;
+  };
+}
+
diff --git a/packages/babel-plugin-transform-react-constant-elements/test/fixtures/constant-elements/pure-expression-3/actual.js b/packages/babel-plugin-transform-react-constant-elements/test/fixtures/constant-elements/pure-expression-3/actual.js
new file mode 100644
index 000000000000..c6b89c77fd1a
--- /dev/null
+++ b/packages/babel-plugin-transform-react-constant-elements/test/fixtures/constant-elements/pure-expression-3/actual.js
@@ -0,0 +1,10 @@
+const OFFSET = 3;
+
+var Foo = React.createClass({
+  render: function () {
+    return (
+      <div tabIndex={OFFSET + 1} />
+    );
+  }
+});
+
diff --git a/packages/babel-plugin-transform-react-constant-elements/test/fixtures/constant-elements/pure-expression-3/expected.js b/packages/babel-plugin-transform-react-constant-elements/test/fixtures/constant-elements/pure-expression-3/expected.js
new file mode 100644
index 000000000000..e709176c4870
--- /dev/null
+++ b/packages/babel-plugin-transform-react-constant-elements/test/fixtures/constant-elements/pure-expression-3/expected.js
@@ -0,0 +1,10 @@
+const OFFSET = 3;
+
+var _ref = <div tabIndex={OFFSET + 1} />;
+
+var Foo = React.createClass({
+  render: function () {
+    return _ref;
+  }
+});
+
diff --git a/packages/babel-plugin-transform-react-constant-elements/test/fixtures/constant-elements/pure-expression/actual.js b/packages/babel-plugin-transform-react-constant-elements/test/fixtures/constant-elements/pure-expression/actual.js
new file mode 100644
index 000000000000..5131c839899b
--- /dev/null
+++ b/packages/babel-plugin-transform-react-constant-elements/test/fixtures/constant-elements/pure-expression/actual.js
@@ -0,0 +1,11 @@
+var Foo = React.createClass({
+  render: function () {
+    return (
+      <div data-text={
+        "Some text, " +
+        "and some more too."
+      } />
+    );
+  }
+});
+
diff --git a/packages/babel-plugin-transform-react-constant-elements/test/fixtures/constant-elements/pure-expression/expected.js b/packages/babel-plugin-transform-react-constant-elements/test/fixtures/constant-elements/pure-expression/expected.js
new file mode 100644
index 000000000000..a7afcb1d6edf
--- /dev/null
+++ b/packages/babel-plugin-transform-react-constant-elements/test/fixtures/constant-elements/pure-expression/expected.js
@@ -0,0 +1,8 @@
+var _ref = <div data-text={"Some text, " + "and some more too."} />;
+
+var Foo = React.createClass({
+  render: function () {
+    return _ref;
+  }
+});
+
diff --git a/packages/babel-plugin-transform-react-display-name/package.json b/packages/babel-plugin-transform-react-display-name/package.json
index 09a05f65e01c..4ae2eb1509a1 100644
--- a/packages/babel-plugin-transform-react-display-name/package.json
+++ b/packages/babel-plugin-transform-react-display-name/package.json
@@ -1,6 +1,6 @@
 {
   "name": "babel-plugin-transform-react-display-name",
-  "version": "6.22.0",
+  "version": "6.23.0",
   "description": "Add displayName to React.createClass calls",
   "repository": "https://github.com/babel/babel/tree/master/packages/babel-plugin-transform-react-display-name",
   "license": "MIT",
diff --git a/packages/babel-plugin-transform-react-jsx/package.json b/packages/babel-plugin-transform-react-jsx/package.json
index 1f6033802360..17391a3be506 100644
--- a/packages/babel-plugin-transform-react-jsx/package.json
+++ b/packages/babel-plugin-transform-react-jsx/package.json
@@ -1,6 +1,6 @@
 {
   "name": "babel-plugin-transform-react-jsx",
-  "version": "6.22.0",
+  "version": "6.23.0",
   "description": "Turn JSX into React function calls",
   "repository": "https://github.com/babel/babel/tree/master/packages/babel-plugin-transform-react-jsx",
   "license": "MIT",
@@ -9,7 +9,7 @@
     "babel-plugin"
   ],
   "dependencies": {
-    "babel-helper-builder-react-jsx": "^6.22.0",
+    "babel-helper-builder-react-jsx": "^6.23.0",
     "babel-plugin-syntax-jsx": "^6.8.0"
   },
   "devDependencies": {
diff --git a/packages/babel-plugin-transform-runtime/package.json b/packages/babel-plugin-transform-runtime/package.json
index 4caf8e695188..98e5430b0783 100644
--- a/packages/babel-plugin-transform-runtime/package.json
+++ b/packages/babel-plugin-transform-runtime/package.json
@@ -1,6 +1,6 @@
 {
   "name": "babel-plugin-transform-runtime",
-  "version": "6.22.0",
+  "version": "6.23.0",
   "description": "Externalise references to helpers and builtins, automatically polyfilling your code without polluting globals",
   "repository": "https://github.com/babel/babel/tree/master/packages/babel-plugin-transform-runtime",
   "license": "MIT",
diff --git a/packages/babel-polyfill/package.json b/packages/babel-polyfill/package.json
index 77a62a8485d9..673e8166fe07 100644
--- a/packages/babel-polyfill/package.json
+++ b/packages/babel-polyfill/package.json
@@ -1,6 +1,6 @@
 {
   "name": "babel-polyfill",
-  "version": "6.22.0",
+  "version": "6.23.0",
   "description": "Provides polyfills necessary for a full ES2015+ environment",
   "author": "Sebastian McKenzie <sebmck@gmail.com>",
   "homepage": "https://babeljs.io/",
diff --git a/packages/babel-preset-flow/.npmignore b/packages/babel-preset-flow/.npmignore
new file mode 100644
index 000000000000..47cdd2c65551
--- /dev/null
+++ b/packages/babel-preset-flow/.npmignore
@@ -0,0 +1,3 @@
+src
+test
+node_modules
diff --git a/packages/babel-preset-flow/README.md b/packages/babel-preset-flow/README.md
new file mode 100644
index 000000000000..26593bd87824
--- /dev/null
+++ b/packages/babel-preset-flow/README.md
@@ -0,0 +1,53 @@
+# babel-preset-flow
+
+> Babel preset for all Flow plugins.
+
+This preset includes the following plugins:
+
+- [transform-flow-strip-types](https://babeljs.io/docs/plugins/transform-flow-strip-types/)
+
+## Example
+
+**In**
+
+```javascript
+function foo(one: any, two: number, three?): string {}
+```
+
+**Out**
+
+```javascript
+function foo(one, two, three) {}
+```
+
+## Installation
+
+```sh
+npm install --save-dev babel-preset-flow
+```
+
+## Usage
+
+### Via `.babelrc` (Recommended)
+
+**.babelrc**
+
+```json
+{
+  "presets": ["flow"]
+}
+```
+
+### Via CLI
+
+```sh
+babel --presets flow script.js
+```
+
+### Via Node API
+
+```javascript
+require("babel-core").transform("code", {
+  presets: ["flow"]
+});
+```
diff --git a/packages/babel-preset-flow/package.json b/packages/babel-preset-flow/package.json
new file mode 100644
index 000000000000..e9f4cb59797e
--- /dev/null
+++ b/packages/babel-preset-flow/package.json
@@ -0,0 +1,18 @@
+{
+  "name": "babel-preset-flow",
+  "version": "6.23.0",
+  "description": "Babel preset for all Flow plugins.",
+  "author": "James Kyle <me@thejameskyle.com>",
+  "repository": "https://github.com/babel/babel/tree/master/packages/babel-preset-flow",
+  "license": "MIT",
+  "main": "lib/index.js",
+  "keywords": [
+    "babel-preset",
+    "flowtype",
+    "flow",
+    "types"
+  ],
+  "dependencies": {
+    "babel-plugin-transform-flow-strip-types": "^6.22.0"
+  }
+}
diff --git a/packages/babel-preset-flow/src/index.js b/packages/babel-preset-flow/src/index.js
new file mode 100644
index 000000000000..8251ca827050
--- /dev/null
+++ b/packages/babel-preset-flow/src/index.js
@@ -0,0 +1,7 @@
+import transformFlowStripTypes from "babel-plugin-transform-flow-strip-types";
+
+export default {
+  plugins: [
+    transformFlowStripTypes
+  ]
+};
diff --git a/packages/babel-preset-react/README.md b/packages/babel-preset-react/README.md
index aceb108affd3..591a59547b89 100644
--- a/packages/babel-preset-react/README.md
+++ b/packages/babel-preset-react/README.md
@@ -2,11 +2,10 @@
 
 > Babel preset for all React plugins.
 
-This preset includes the following plugins:
+This preset includes the following plugins/presets:
 
-- [syntax-flow](https://babeljs.io/docs/plugins/syntax-flow/)
+- [preset-flow](https://babeljs.io/docs/plugins/preset-flow/)
 - [syntax-jsx](https://babeljs.io/docs/plugins/syntax-jsx/)
-- [transform-flow-strip-types](https://babeljs.io/docs/plugins/transform-flow-strip-types/)
 - [transform-react-jsx](https://babeljs.io/docs/plugins/transform-react-jsx/)
 - [transform-react-display-name](https://babeljs.io/docs/plugins/transform-react-display-name/)
 
diff --git a/packages/babel-preset-react/package.json b/packages/babel-preset-react/package.json
index 378b3a04563d..1a4bf7c55d52 100644
--- a/packages/babel-preset-react/package.json
+++ b/packages/babel-preset-react/package.json
@@ -1,6 +1,6 @@
 {
   "name": "babel-preset-react",
-  "version": "6.22.0",
+  "version": "6.23.0",
   "description": "Babel preset for all React plugins.",
   "author": "Sebastian McKenzie <sebmck@gmail.com>",
   "homepage": "https://babeljs.io/",
@@ -8,11 +8,10 @@
   "repository": "https://github.com/babel/babel/tree/master/packages/babel-preset-react",
   "main": "lib/index.js",
   "dependencies": {
-    "babel-plugin-syntax-flow": "^6.3.13",
+    "babel-preset-flow": "^6.23.0",
     "babel-plugin-syntax-jsx": "^6.3.13",
-    "babel-plugin-transform-flow-strip-types": "^6.22.0",
-    "babel-plugin-transform-react-display-name": "^6.22.0",
-    "babel-plugin-transform-react-jsx": "^6.22.0",
+    "babel-plugin-transform-react-display-name": "^6.23.0",
+    "babel-plugin-transform-react-jsx": "^6.23.0",
     "babel-plugin-transform-react-jsx-source": "^6.22.0",
     "babel-plugin-transform-react-jsx-self": "^6.22.0"
   }
diff --git a/packages/babel-preset-react/src/index.js b/packages/babel-preset-react/src/index.js
index 55dd6bbd8d54..361238658ef9 100644
--- a/packages/babel-preset-react/src/index.js
+++ b/packages/babel-preset-react/src/index.js
@@ -1,6 +1,5 @@
+import presetFlow from "babel-preset-flow";
 import transformReactJSX from "babel-plugin-transform-react-jsx";
-import transformFlowStripTypes from "babel-plugin-transform-flow-strip-types";
-import transformSyntaxFlow from "babel-plugin-syntax-flow";
 import transformSyntaxJSX from "babel-plugin-syntax-jsx";
 import transformReactDisplayName from "babel-plugin-transform-react-display-name";
 
@@ -9,10 +8,11 @@ import transformReactDisplayName from "babel-plugin-transform-react-display-name
 // import transformReactJSXSelf from "babel-plugin-transform-react-jsx-self";
 
 export default {
+  presets: [
+    presetFlow
+  ],
   plugins: [
     transformReactJSX,
-    transformFlowStripTypes,
-    transformSyntaxFlow,
     transformSyntaxJSX,
     transformReactDisplayName
   ],
diff --git a/packages/babel-register/package.json b/packages/babel-register/package.json
index 0ace0ca3b829..e6e328efc57d 100644
--- a/packages/babel-register/package.json
+++ b/packages/babel-register/package.json
@@ -1,6 +1,6 @@
 {
   "name": "babel-register",
-  "version": "6.22.0",
+  "version": "6.23.0",
   "description": "babel require hook",
   "license": "MIT",
   "repository": "https://github.com/babel/babel/tree/master/packages/babel-register",
@@ -8,7 +8,7 @@
   "main": "lib/node.js",
   "browser": "lib/browser.js",
   "dependencies": {
-    "babel-core": "^6.22.0",
+    "babel-core": "^6.23.0",
     "core-js": "^2.4.0",
     "home-or-tmp": "^3.0.0",
     "lodash": "^4.2.0",
diff --git a/packages/babel-template/package.json b/packages/babel-template/package.json
index 8c36f1655b22..d75b97caaf86 100644
--- a/packages/babel-template/package.json
+++ b/packages/babel-template/package.json
@@ -1,6 +1,6 @@
 {
   "name": "babel-template",
-  "version": "6.22.0",
+  "version": "6.23.0",
   "description": "Generate an AST from a string template.",
   "author": "Sebastian McKenzie <sebmck@gmail.com>",
   "homepage": "https://babeljs.io/",
@@ -9,8 +9,8 @@
   "main": "lib/index.js",
   "dependencies": {
     "babylon": "^6.11.0",
-    "babel-traverse": "^6.22.0",
-    "babel-types": "^6.22.0",
+    "babel-traverse": "^6.23.0",
+    "babel-types": "^6.23.0",
     "lodash": "^4.2.0"
   }
 }
diff --git a/packages/babel-traverse/package.json b/packages/babel-traverse/package.json
index 51dff4bfd716..40de088ff39c 100644
--- a/packages/babel-traverse/package.json
+++ b/packages/babel-traverse/package.json
@@ -1,6 +1,6 @@
 {
   "name": "babel-traverse",
-  "version": "6.22.1",
+  "version": "6.23.1",
   "description": "The Babel Traverse module maintains the overall tree state, and is responsible for replacing, removing, and adding nodes",
   "author": "Sebastian McKenzie <sebmck@gmail.com>",
   "homepage": "https://babeljs.io/",
@@ -9,8 +9,8 @@
   "main": "lib/index.js",
   "dependencies": {
     "babel-code-frame": "^6.22.0",
-    "babel-messages": "^6.22.0",
-    "babel-types": "^6.22.0",
+    "babel-messages": "^6.23.0",
+    "babel-types": "^6.23.0",
     "babylon": "^6.15.0",
     "debug": "^2.2.0",
     "globals": "^9.0.0",
@@ -18,6 +18,6 @@
     "lodash": "^4.2.0"
   },
   "devDependencies": {
-    "babel-generator": "^6.22.0"
+    "babel-generator": "^6.23.0"
   }
 }
diff --git a/packages/babel-traverse/src/path/lib/hoister.js b/packages/babel-traverse/src/path/lib/hoister.js
index 93b9323bd35d..69154bbc2d27 100644
--- a/packages/babel-traverse/src/path/lib/hoister.js
+++ b/packages/babel-traverse/src/path/lib/hoister.js
@@ -2,11 +2,27 @@ import { react } from "babel-types";
 import * as t from "babel-types";
 
 const referenceVisitor = {
+  // This visitor looks for bindings to establish a topmost scope for hoisting.
   ReferencedIdentifier(path, state) {
-    if (path.isJSXIdentifier() && react.isCompatTag(path.node.name)) {
+    // Don't hoist regular JSX identifiers ('div', 'span', etc).
+    // We do have to consider member expressions for hoisting (e.g. `this.component`)
+    if (
+      path.isJSXIdentifier() &&
+      react.isCompatTag(path.node.name) &&
+      !path.parentPath.isJSXMemberExpression()
+    ) {
       return;
     }
 
+    // If the identifier refers to `this`, we need to break on the closest non-arrow scope.
+    if (path.node.name === "this") {
+      let scope = path.scope;
+      do {
+        if (scope.path.isFunction() && !scope.path.isArrowFunctionExpression()) break;
+      } while (scope = scope.parent);
+      if (scope) state.breakOnScopePaths.push(scope.path);
+    }
+
     // direct references that we need to track to hoist this to the highest scope we can
     const binding = path.scope.getBinding(path.node.name);
     if (!binding) return;
@@ -15,25 +31,27 @@ const referenceVisitor = {
     // eg. it's in a closure etc
     if (binding !== state.scope.getBinding(path.node.name)) return;
 
-    if (binding.constant) {
-      state.bindings[path.node.name] = binding;
-    } else {
-      for (const violationPath of (binding.constantViolations: Array)) {
-        state.breakOnScopePaths = state.breakOnScopePaths.concat(violationPath.getAncestry());
-      }
-    }
+    state.bindings[path.node.name] = binding;
   }
 };
 
 export default class PathHoister {
   constructor(path, scope) {
+    // Storage for scopes we can't hoist above.
     this.breakOnScopePaths = [];
+    // Storage for bindings that may affect what path we can hoist to.
     this.bindings          = {};
+    // Storage for eligible scopes.
     this.scopes            = [];
+    // Our original scope and path.
     this.scope             = scope;
     this.path              = path;
+    // By default, we attach as far up as we can; but if we're trying
+    // to avoid referencing a binding, we may have to go after.
+    this.attachAfter       = false;
   }
 
+  // A scope is compatible if all required bindings are reachable.
   isCompatibleScope(scope) {
     for (const key in this.bindings) {
       const binding = this.bindings[key];
@@ -45,6 +63,7 @@ export default class PathHoister {
     return true;
   }
 
+  // Look through all scopes and push compatible ones.
   getCompatibleScopes() {
     let scope = this.path.scope;
     do {
@@ -54,6 +73,7 @@ export default class PathHoister {
         break;
       }
 
+      // deopt: These scopes are set in the visitor on const violations
       if (this.breakOnScopePaths.indexOf(scope.path) >= 0) {
         break;
       }
@@ -61,7 +81,7 @@ export default class PathHoister {
   }
 
   getAttachmentPath() {
-    const path = this._getAttachmentPath();
+    let path = this._getAttachmentPath();
     if (!path) return;
 
     let targetScope = path.scope;
@@ -82,8 +102,18 @@ export default class PathHoister {
         // allow parameter references
         if (binding.kind === "param") continue;
 
-        // if this binding appears after our attachment point then don't hoist it
-        if (this.getAttachmentParentForPath(binding.path).key > path.key) return;
+        // if this binding appears after our attachment point, then we move after it.
+        if (this.getAttachmentParentForPath(binding.path).key > path.key) {
+          this.attachAfter = true;
+          path = binding.path;
+
+          // We also move past any constant violations.
+          for (const violationPath of (binding.constantViolations: Array)) {
+            if (this.getAttachmentParentForPath(violationPath).key > path.key) {
+              path = violationPath;
+            }
+          }
+        }
       }
     }
 
@@ -94,11 +124,12 @@ export default class PathHoister {
     const scopes = this.scopes;
 
     const scope = scopes.pop();
+    // deopt: no compatible scopes
     if (!scope) return;
 
     if (scope.path.isFunction()) {
       if (this.hasOwnParamBindings(scope)) {
-        // should ignore this scope since it's ourselves
+        // deopt: should ignore this scope since it's ourselves
         if (this.scope === scope) return;
 
         // needs to be attached to the body
@@ -117,26 +148,30 @@ export default class PathHoister {
     if (scope) return this.getAttachmentParentForPath(scope.path);
   }
 
+  // Find an attachment for this path.
   getAttachmentParentForPath(path) {
     do {
-      if (!path.parentPath ||
-          (Array.isArray(path.container) && path.isStatement()) ||
-          (
-            path.isVariableDeclarator() &&
-            path.parentPath.node !== null &&
-            path.parentPath.node.declarations.length > 1
-          )
-      )
+      if (
+        // Beginning of the scope
+        !path.parentPath ||
+        // Has siblings and is a statement
+        (Array.isArray(path.container) && path.isStatement()) ||
+        // Is part of multiple var declarations
+        (path.isVariableDeclarator() &&
+          path.parentPath.node !== null &&
+          path.parentPath.node.declarations.length > 1))
         return path;
     } while ((path = path.parentPath));
   }
 
+  // Returns true if a scope has param bindings.
   hasOwnParamBindings(scope) {
     for (const name in this.bindings) {
       if (!scope.hasOwnBinding(name)) continue;
 
       const binding = this.bindings[name];
-      if (binding.kind === "param") return true;
+      // Ensure constant; without it we could place behind a reassignment
+      if (binding.kind === "param" && binding.constant) return true;
     }
     return false;
   }
@@ -161,7 +196,8 @@ export default class PathHoister {
     let uid = attachTo.scope.generateUidIdentifier("ref");
     const declarator = t.variableDeclarator(uid, this.path.node);
 
-    attachTo.insertBefore([
+    const insertFn = this.attachAfter ? "insertAfter" : "insertBefore";
+    attachTo[insertFn]([
       attachTo.isVariableDeclarator() ? declarator : t.variableDeclaration("var", [declarator])
     ]);
 
diff --git a/packages/babel-types/README.md b/packages/babel-types/README.md
index 13b2ec3a5a64..683388362925 100644
--- a/packages/babel-types/README.md
+++ b/packages/babel-types/README.md
@@ -930,6 +930,7 @@ Aliases: `ModuleSpecifier`
 
  - `local`: `Identifier` (required)
  - `imported`: `Identifier` (required)
+ - `importKind`: `null | 'type' | 'typeof'` (default: `null`)
 
 ---
 
diff --git a/packages/babel-types/package.json b/packages/babel-types/package.json
index 57c4bc762a15..5ed4524a29b6 100644
--- a/packages/babel-types/package.json
+++ b/packages/babel-types/package.json
@@ -1,6 +1,6 @@
 {
   "name": "babel-types",
-  "version": "6.22.0",
+  "version": "6.23.0",
   "description": "Babel Types is a Lodash-esque utility library for AST nodes",
   "author": "Sebastian McKenzie <sebmck@gmail.com>",
   "homepage": "https://babeljs.io/",