Reduce dependency on lodash functions: values, extends (#11798)

* Replace lodash 'values' usage with Object.keys => .map(obj[key])

* Block scoping: refactor letReferences, outsideLetReferences as objects of type Map

* Remove lodash dependency from babel-plugin-transform-block-scoping

* Fixup: Add missing Object.keys call

* Fixup: Update remaining property accessors

* Coerce Map.values() iterator results into an array via spread operator

* Fixup: Map.put -> Map.set

* Fixup: undo incorrect variable de-duplication

* Replace array-spread-plus-map combination with Array.from call

* Extract an extendMap function as an attempt to create an optimization boundary

* Experiment: cast objects to string (eliminates one Map/object difference per https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Map )

* Fixup: perform String cast on map keys, not values

* Revert "Fixup: perform String cast on map keys, not values"

This reverts commit abdd147.

* Revert "Experiment: cast objects to string (eliminates one Map/object difference per https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Map )"

This reverts commit a4035c8.

* Experiment: filter keys via Object.prototype.hasOwnProperty.call

* Revert "Experiment: filter keys via Object.prototype.hasOwnProperty.call"

This reverts commit 491c093.

* Migrate back from Map-based reference storage to Object-based storage; access performance appears much improved for Object property access

* Revert "Migrate back from Map-based reference storage to Object-based storage; access performance appears much improved for Object property access"

This reverts commit 2119acc.

* Iterate over a clone of outsideRefs keys

* Revert "Extract an extendMap function as an attempt to create an optimization boundary"

This reverts commit 85689f2.

* Fixup: migrate remaining Object property access to Map.get in tdz module

packages/babel-plugin-transform-block-scoping/package.json

@@ -13,8 +13,7 @@
   },
   "main": "lib/index.js",
   "dependencies": {
-    "@babel/helper-plugin-utils": "^7.10.4",
-    "lodash": "^4.17.13"
+    "@babel/helper-plugin-utils": "^7.10.4"
   },
   "keywords": [
     "babel-plugin"

packages/babel-plugin-transform-block-scoping/src/index.js

@@ -2,8 +2,6 @@ import { declare } from "@babel/helper-plugin-utils";
 import type NodePath from "@babel/traverse";
 import type Scope from "@babel/traverse";
 import { visitor as tdzVisitor } from "./tdz";
-import values from "lodash/values";
-import extend from "lodash/extend";
 import { traverse, template, types as t } from "@babel/core";
 
 const DONE = new WeakSet();
@@ -195,7 +193,7 @@ const letReferenceBlockVisitor = traverse.visitors.merge([
 const letReferenceFunctionVisitor = traverse.visitors.merge([
   {
     ReferencedIdentifier(path, state) {
-      const ref = state.letReferences[path.node.name];
+      const ref = state.letReferences.get(path.node.name);
 
       // not a part of our scope
       if (!ref) return;
@@ -250,7 +248,7 @@ const continuationVisitor = {
     if (path.isAssignmentExpression() || path.isUpdateExpression()) {
       for (const name of Object.keys(path.getBindingIdentifiers())) {
         if (
-          state.outsideReferences[name] !==
+          state.outsideReferences.get(name) !==
           path.scope.getBindingIdentifier(name)
         ) {
           continue;
@@ -359,9 +357,9 @@ class BlockScoping {
     this.blockPath = blockPath;
     this.block = blockPath.node;
 
-    this.outsideLetReferences = Object.create(null);
+    this.outsideLetReferences = new Map();
     this.hasLetReferences = false;
-    this.letReferences = Object.create(null);
+    this.letReferences = new Map();
     this.body = [];
 
     if (loopPath) {
@@ -447,8 +445,8 @@ class BlockScoping {
       blockScope.getFunctionParent() || blockScope.getProgramParent();
     const letRefs = this.letReferences;
 
-    for (const key of Object.keys(letRefs)) {
-      const ref = letRefs[key];
+    for (const key of letRefs.keys()) {
+      const ref = letRefs.get(key);
       const binding = blockScope.getBinding(ref.name);
       if (!binding) continue;
       if (binding.kind === "let" || binding.kind === "const") {
@@ -476,10 +474,10 @@ class BlockScoping {
     // those in upper scopes and then if they do, generate a uid
     // for them and replace all references with it
 
-    for (const key of Object.keys(letRefs)) {
+    for (const key of letRefs.keys()) {
       // just an Identifier node we collected in `getLetReferences`
       // this is the defining identifier of a declaration
-      const ref = letRefs[key];
+      const ref = letRefs.get(key);
 
       // todo: could skip this if the colliding binding is in another function
       if (scope.parentHasBinding(key) || scope.hasGlobal(key)) {
@@ -496,8 +494,8 @@ class BlockScoping {
       }
     }
 
-    for (const key of Object.keys(outsideLetRefs)) {
-      const ref = letRefs[key];
+    for (const key of outsideLetRefs.keys()) {
+      const ref = letRefs.get(key);
       // check for collisions with a for loop's init variable and the enclosing scope's bindings
       // https://github.com/babel/babel/issues/8498
       if (isInLoop(this.blockPath) && blockPathScope.hasOwnBinding(key)) {
@@ -519,20 +517,21 @@ class BlockScoping {
 
     // remap loop heads with colliding variables
     if (this.loop) {
-      for (const name of Object.keys(outsideRefs)) {
-        const id = outsideRefs[name];
+      // nb: clone outsideRefs keys since the map is modified within the loop
+      for (const name of [...outsideRefs.keys()]) {
+        const id = outsideRefs.get(name);
 
         if (
           this.scope.hasGlobal(id.name) ||
           this.scope.parentHasBinding(id.name)
         ) {
-          delete outsideRefs[id.name];
-          delete this.letReferences[id.name];
+          outsideRefs.delete(id.name);
+          this.letReferences.delete(id.name);
 
           this.scope.rename(id.name);
 
-          this.letReferences[id.name] = id;
-          outsideRefs[id.name] = id;
+          this.letReferences.set(id.name, id);
+          outsideRefs.set(id.name, id);
         }
       }
     }
@@ -545,7 +544,7 @@ class BlockScoping {
     this.hoistVarDeclarations();
 
     // turn outsideLetReferences into an array
-    const args = values(outsideRefs).map(id => t.cloneNode(id));
+    const args = Array.from(outsideRefs.values(), node => t.cloneNode(node));
     const params = args.map(id => t.cloneNode(id));
 
     const isSwitch = this.blockPath.isSwitchStatement();
@@ -702,7 +701,10 @@ class BlockScoping {
       const init = this.loop.left || this.loop.init;
       if (isBlockScoped(init)) {
         declarators.push(init);
-        extend(this.outsideLetReferences, t.getBindingIdentifiers(init));
+        const names = t.getBindingIdentifiers(init);
+        for (const name of Object.keys(names)) {
+          this.outsideLetReferences.set(name, names[name]);
+        }
       }
     }
 
@@ -751,7 +753,9 @@ class BlockScoping {
       // declaration, rather than (for example) mistakenly including the
       // parameters of a function declaration. Fixes #4880.
       const keys = t.getBindingIdentifiers(declar, false, true);
-      extend(this.letReferences, keys);
+      for (const key of Object.keys(keys)) {
+        this.letReferences.set(key, keys[key]);
+      }
       this.hasLetReferences = true;
     }
 

packages/babel-plugin-transform-block-scoping/src/tdz.js

@@ -20,7 +20,7 @@ function buildTDZAssert(node, state) {
 }
 
 function isReference(node, scope, state) {
-  const declared = state.letReferences[node.name];
+  const declared = state.letReferences.get(node.name);
   if (!declared) return false;
 
   // declared node is different in this scope