Add "allowArrayLike" support to the for-of transform

packages/babel-helpers/src/helpers.js

@@ -1079,10 +1079,16 @@ helpers.createForOfIteratorHelper = helper("7.9.0")`
   // e: error (called whenever something throws)
   // f: finish (always called at the end)
 
-  export default function _createForOfIteratorHelper(o) {
+  export default function _createForOfIteratorHelper(o, allowArrayLike) {
+    var it;
     if (typeof Symbol === "undefined" || o[Symbol.iterator] == null) {
       // Fallback for engines without symbol support
-      if (Array.isArray(o) || (o = unsupportedIterableToArray(o))) {
+      if (
+        Array.isArray(o) ||
+        (it = unsupportedIterableToArray(o)) ||
+        (allowArrayLike && o && typeof o.length === "number")
+      ) {
+        if (it) o = it;
         var i = 0;
         var F = function(){};
         return {
@@ -1099,7 +1105,7 @@ helpers.createForOfIteratorHelper = helper("7.9.0")`
       throw new TypeError("Invalid attempt to iterate non-iterable instance.\\nIn order to be iterable, non-array objects must have a [Symbol.iterator]() method.");
     }
 
-    var it, normalCompletion = true, didErr = false, err;
+    var normalCompletion = true, didErr = false, err;
 
     return {
       s() {
@@ -1128,22 +1134,29 @@ helpers.createForOfIteratorHelper = helper("7.9.0")`
 helpers.createForOfIteratorHelperLoose = helper("7.9.0")`
   import unsupportedIterableToArray from "unsupportedIterableToArray";
 
-  export default function _createForOfIteratorHelperLoose(o) {
-    var i = 0;
+  export default function _createForOfIteratorHelperLoose(o, allowArrayLike) {
+    var it;
 
     if (typeof Symbol === "undefined" || o[Symbol.iterator] == null) {
       // Fallback for engines without symbol support
-      if (Array.isArray(o) || (o = unsupportedIterableToArray(o)))
+      if (
+        Array.isArray(o) ||
+        (it = unsupportedIterableToArray(o)) ||
+        (allowArrayLike && o && typeof o.length === "number")
+      ) {
+        if (it) o = it;
+        var i = 0;
         return function() {
           if (i >= o.length) return { done: true };
           return { done: false, value: o[i++] };
         }
+      }
 
       throw new TypeError("Invalid attempt to iterate non-iterable instance.\\nIn order to be iterable, non-array objects must have a [Symbol.iterator]() method.");
     }
 
-    i = o[Symbol.iterator]();
-    return i.next.bind(i);
+    it = o[Symbol.iterator]();
+    return it.next.bind(it);
   }
 `;
 

packages/babel-plugin-transform-for-of/src/index.js

@@ -6,14 +6,20 @@ import transformWithoutHelper from "./no-helper-implementation";
 export default declare((api, options) => {
   api.assertVersion(7);
 
-  const { loose, assumeArray } = options;
+  const { loose, assumeArray, allowArrayLike } = options;
 
   if (loose === true && assumeArray === true) {
     throw new Error(
       `The loose and assumeArray options cannot be used together in @babel/plugin-transform-for-of`,
     );
   }
 
+  if (assumeArray === true && allowArrayLike === true) {
+    throw new Error(
+      `The assumeArray and allowArrayLike options cannot be used together in @babel/plugin-transform-for-of`,
+    );
+  }
+
   if (assumeArray) {
     return {
       name: "transform-for-of",
@@ -86,12 +92,12 @@ export default declare((api, options) => {
   `);
 
   const buildForOfLoose = template.statements(`
-    for (var ITERATOR_HELPER = CREATE_ITERATOR_HELPER(OBJECT), STEP_KEY;
+    for (var ITERATOR_HELPER = CREATE_ITERATOR_HELPER(OBJECT, ALLOW_ARRAY_LIKE), STEP_KEY;
         !(STEP_KEY = ITERATOR_HELPER()).done;) BODY;
   `);
 
   const buildForOf = template.statements(`
-    var ITERATOR_HELPER = CREATE_ITERATOR_HELPER(OBJECT), STEP_KEY;
+    var ITERATOR_HELPER = CREATE_ITERATOR_HELPER(OBJECT, ALLOW_ARRAY_LIKE), STEP_KEY;
     try {
       for (ITERATOR_HELPER.s(); !(STEP_KEY = ITERATOR_HELPER.n()).done;) BODY;
     } catch (err) {
@@ -200,6 +206,7 @@ export default declare((api, options) => {
         const nodes = builder.build({
           CREATE_ITERATOR_HELPER: state.addHelper(builder.helper),
           ITERATOR_HELPER: scope.generateUidIdentifier("iterator"),
+          ALLOW_ARRAY_LIKE: allowArrayLike ? t.booleanLiteral(true) : null,
           STEP_KEY: t.identifier(stepKey),
           OBJECT: node.right,
           BODY: node.body,

packages/babel-plugin-transform-for-of/test/fixtures/loose-allowArrayLike/holes/exec.js

@@ -0,0 +1,7 @@
+var p2 = { 0: "a", 2: "c", length: 3 };
+
+var arr = [];
+for (var x of p2) arr.push(x);
+
+expect(arr).toEqual(["a", undefined, "c"]);
+expect(1 in arr).toBe(true); // Not holey

packages/babel-plugin-transform-for-of/test/fixtures/loose-allowArrayLike/holes/options.json

@@ -0,0 +1,6 @@
+{
+  "plugins": [
+    ["external-helpers", { "helperVersion": "7.100.0" }],
+    ["transform-for-of", { "loose": true, "allowArrayLike": true }]
+  ]
+}

packages/babel-plugin-transform-for-of/test/fixtures/loose-allowArrayLike/length-cropped/exec.js

@@ -0,0 +1,6 @@
+var p2 = { 0: "b", 1: "c", 2: "d", length: 2 };
+
+var arr = [];
+for (var x of p2) arr.push(x);
+
+expect(arr).toEqual(["b", "c"]);

packages/babel-plugin-transform-for-of/test/fixtures/loose-allowArrayLike/length-cropped/options.json

@@ -0,0 +1,6 @@
+{
+  "plugins": [
+    ["external-helpers", { "helperVersion": "7.100.0" }],
+    ["transform-for-of", { "loose": true, "allowArrayLike": true }]
+  ]
+}

packages/babel-plugin-transform-for-of/test/fixtures/loose-allowArrayLike/simple/exec.js

@@ -0,0 +1,6 @@
+var p2 = { 0: "b", 1: "c", 2: "d", length: 3 };
+
+var arr = [];
+for (var x of p2) arr.push(x);
+
+expect(arr).toEqual(["b", "c", "d"]);

packages/babel-plugin-transform-for-of/test/fixtures/loose-allowArrayLike/simple/input.js

@@ -0,0 +1 @@
+for (var x of p2) arr.push(x);

packages/babel-plugin-transform-for-of/test/fixtures/loose-allowArrayLike/simple/options.json

@@ -0,0 +1,6 @@
+{
+  "plugins": [
+    ["external-helpers", { "helperVersion": "7.100.0" }],
+    ["transform-for-of", { "loose": true, "allowArrayLike": true }]
+  ]
+}

packages/babel-plugin-transform-for-of/test/fixtures/loose-allowArrayLike/simple/output.js

@@ -0,0 +1,4 @@
+for (var _iterator = babelHelpers.createForOfIteratorHelperLoose(p2, true), _step; !(_step = _iterator()).done;) {
+  var x = _step.value;
+  arr.push(x);
+}

packages/babel-plugin-transform-for-of/test/fixtures/spec-allowArrayLike/holes/exec.js

@@ -0,0 +1,7 @@
+var p2 = { 0: "a", 2: "c", length: 3 };
+
+var arr = [];
+for (var x of p2) arr.push(x);
+
+expect(arr).toEqual(["a", undefined, "c"]);
+expect(1 in arr).toBe(true); // Not holey

packages/babel-plugin-transform-for-of/test/fixtures/spec-allowArrayLike/holes/options.json

@@ -0,0 +1,6 @@
+{
+  "plugins": [
+    ["external-helpers", { "helperVersion": "7.100.0" }],
+    ["transform-for-of", { "allowArrayLike": true }]
+  ]
+}

packages/babel-plugin-transform-for-of/test/fixtures/spec-allowArrayLike/length-cropped/exec.js

@@ -0,0 +1,6 @@
+var p2 = { 0: "b", 1: "c", 2: "d", length: 2 };
+
+var arr = [];
+for (var x of p2) arr.push(x);
+
+expect(arr).toEqual(["b", "c"]);

packages/babel-plugin-transform-for-of/test/fixtures/spec-allowArrayLike/length-cropped/options.json

@@ -0,0 +1,6 @@
+{
+  "plugins": [
+    ["external-helpers", { "helperVersion": "7.100.0" }],
+    ["transform-for-of", { "allowArrayLike": true }]
+  ]
+}

packages/babel-plugin-transform-for-of/test/fixtures/spec-allowArrayLike/simple/exec.js

@@ -0,0 +1,6 @@
+var p2 = { 0: "b", 1: "c", 2: "d", length: 3 };
+
+var arr = [];
+for (var x of p2) arr.push(x);
+
+expect(arr).toEqual(["b", "c", "d"]);

packages/babel-plugin-transform-for-of/test/fixtures/spec-allowArrayLike/simple/input.js

@@ -0,0 +1 @@
+for (var x of p2) arr.push(x);

packages/babel-plugin-transform-for-of/test/fixtures/spec-allowArrayLike/simple/options.json

@@ -0,0 +1,6 @@
+{
+  "plugins": [
+    ["external-helpers", { "helperVersion": "7.100.0" }],
+    ["transform-for-of", { "allowArrayLike": true }]
+  ]
+}

packages/babel-plugin-transform-for-of/test/fixtures/spec-allowArrayLike/simple/output.js

@@ -0,0 +1,13 @@
+var _iterator = babelHelpers.createForOfIteratorHelper(p2, true),
+    _step;
+
+try {
+  for (_iterator.s(); !(_step = _iterator.n()).done;) {
+    var x = _step.value;
+    arr.push(x);
+  }
+} catch (err) {
+  _iterator.e(err);
+} finally {
+  _iterator.f();
+}

packages/babel-preset-env/test/fixtures/sanity/block-scoping-for-of/output.js

@@ -6,7 +6,7 @@ function _iterableToArrayLimit(arr, i) { if (typeof Symbol === "undefined" || !(
 
 function _arrayWithHoles(arr) { if (Array.isArray(arr)) return arr; }
 
-function _createForOfIteratorHelper(o) { if (typeof Symbol === "undefined" || o[Symbol.iterator] == null) { if (Array.isArray(o) || (o = _unsupportedIterableToArray(o))) { var i = 0; var F = function F() {}; return { s: F, n: function n() { if (i >= o.length) return { done: true }; return { done: false, value: o[i++] }; }, e: function e(_e) { throw _e; }, f: F }; } throw new TypeError("Invalid attempt to iterate non-iterable instance.\nIn order to be iterable, non-array objects must have a [Symbol.iterator]() method."); } var it, normalCompletion = true, didErr = false, err; return { s: function s() { it = o[Symbol.iterator](); }, n: function n() { var step = it.next(); normalCompletion = step.done; return step; }, e: function e(_e2) { didErr = true; err = _e2; }, f: function f() { try { if (!normalCompletion && it["return"] != null) it["return"](); } finally { if (didErr) throw err; } } }; }
+function _createForOfIteratorHelper(o, allowArrayLike) { var it; if (typeof Symbol === "undefined" || o[Symbol.iterator] == null) { if (Array.isArray(o) || (it = _unsupportedIterableToArray(o)) || allowArrayLike && o && typeof o.length === "number") { if (it) o = it; var i = 0; var F = function F() {}; return { s: F, n: function n() { if (i >= o.length) return { done: true }; return { done: false, value: o[i++] }; }, e: function e(_e) { throw _e; }, f: F }; } throw new TypeError("Invalid attempt to iterate non-iterable instance.\nIn order to be iterable, non-array objects must have a [Symbol.iterator]() method."); } var normalCompletion = true, didErr = false, err; return { s: function s() { it = o[Symbol.iterator](); }, n: function n() { var step = it.next(); normalCompletion = step.done; return step; }, e: function e(_e2) { didErr = true; err = _e2; }, f: function f() { try { if (!normalCompletion && it["return"] != null) it["return"](); } finally { if (didErr) throw err; } } }; }
 
 function _unsupportedIterableToArray(o, minLen) { if (!o) return; if (typeof o === "string") return _arrayLikeToArray(o, minLen); var n = Object.prototype.toString.call(o).slice(8, -1); if (n === "Object" && o.constructor) n = o.constructor.name; if (n === "Map" || n === "Set") return Array.from(n); if (n === "Arguments" || /^(?:Ui|I)nt(?:8|16|32)(?:Clamped)?Array$/.test(n)) return _arrayLikeToArray(o, minLen); }