Support iterating generators in browsers without Symbol

packages/babel-helpers/src/helpers.js

@@ -83,18 +83,15 @@ helpers.jsx = helper("7.0.0-beta.0")`
 
 helpers.asyncIterator = helper("7.0.0-beta.0")`
   export default function _asyncIterator(iterable) {
-    var method
+    var method;
     if (typeof Symbol !== "undefined") {
-      if (Symbol.asyncIterator) {
-        method = iterable[Symbol.asyncIterator]
-        if (method != null) return method.call(iterable);
-      }
-      if (Symbol.iterator) {
-        method = iterable[Symbol.iterator]
-        if (method != null) return method.call(iterable);
-      }
+      if (Symbol.asyncIterator) method = iterable[Symbol.asyncIterator];
+      if (method == null && Symbol.iterator) method = iterable[Symbol.iterator];
     }
-    throw new TypeError("Object is not async iterable");
+    if (method == null) method = iterable["@@asyncIterator"];
+    if (method == null) method = iterable["@@iterator"]
+    if (method == null) throw new TypeError("Object is not async iterable");
+    return method.call(iterable);
   }
 `;
 
@@ -179,9 +176,7 @@ helpers.AsyncGenerator = helper("7.0.0-beta.0")`
     }
   }
 
-  if (typeof Symbol === "function" && Symbol.asyncIterator) {
-    AsyncGenerator.prototype[Symbol.asyncIterator] = function () { return this; };
-  }
+  AsyncGenerator.prototype[typeof Symbol === "function" && Symbol.asyncIterator || "@@asyncIterator"] = function () { return this; };
 
   AsyncGenerator.prototype.next = function (arg) { return this._invoke("next", arg); };
   AsyncGenerator.prototype.throw = function (arg) { return this._invoke("throw", arg); };
@@ -216,9 +211,7 @@ helpers.asyncGeneratorDelegate = helper("7.0.0-beta.0")`
       return { done: false, value: awaitWrap(value) };
     };
 
-    if (typeof Symbol === "function" && Symbol.iterator) {
-      iter[Symbol.iterator] = function () { return this; };
-    }
+    iter[typeof Symbol !== "undefined" && Symbol.iterator || "@@iterator"] = function () { return this; };
 
     iter.next = function (value) {
       if (waiting) {
@@ -1003,7 +996,7 @@ helpers.maybeArrayLike = helper("7.9.0")`
 
 helpers.iterableToArray = helper("7.0.0-beta.0")`
   export default function _iterableToArray(iter) {
-    if (typeof Symbol !== "undefined" && Symbol.iterator in Object(iter)) return Array.from(iter);
+    if (typeof Symbol !== "undefined" && iter[Symbol.iterator] != null || iter["@@iterator"] != null) return Array.from(iter);
   }
 `;
 
@@ -1019,14 +1012,15 @@ helpers.iterableToArrayLimit = helper("7.0.0-beta.0")`
     // _i = _iterator
     // _s = _step
 
-    if (typeof Symbol === "undefined" || !(Symbol.iterator in Object(arr))) return;
+    var _i = arr && (typeof Symbol !== "undefined" && arr[Symbol.iterator] || arr["@@iterator"]);
+    if (_i == null) return;
 
     var _arr = [];
     var _n = true;
     var _d = false;
     var _e = undefined;
     try {
-      for (var _i = arr[Symbol.iterator](), _s; !(_n = (_s = _i.next()).done); _n = true) {
+      for (_i = _i.call(arr), _s; !(_n = (_s = _i.next()).done); _n = true) {
         _arr.push(_s.value);
         if (i && _arr.length === i) break;
       }
@@ -1046,10 +1040,11 @@ helpers.iterableToArrayLimit = helper("7.0.0-beta.0")`
 
 helpers.iterableToArrayLimitLoose = helper("7.0.0-beta.0")`
   export default function _iterableToArrayLimitLoose(arr, i) {
-    if (typeof Symbol === "undefined" || !(Symbol.iterator in Object(arr))) return;
+    var _i = arr && (typeof Symbol !== "undefined" && arr[Symbol.iterator] || arr["@@iterator"]);
+    if (_i == null) return;
 
     var _arr = [];
-    for (var _iterator = arr[Symbol.iterator](), _step; !(_step = _iterator.next()).done;) {
+    for (_i = _i.call(arr), _step; !(_step = _i.next()).done;) {
       _arr.push(_step.value);
       if (i && _arr.length === i) break;
     }
@@ -1104,8 +1099,9 @@ helpers.createForOfIteratorHelper = helper("7.9.0")`
   // f: finish (always called at the end)
 
   export default function _createForOfIteratorHelper(o, allowArrayLike) {
-    var it;
-    if (typeof Symbol === "undefined" || o[Symbol.iterator] == null) {
+    var it = typeof Symbol !== "undefined" && o[Symbol.iterator] || o["@@iterator"];
+
+    if (!it) {
       // Fallback for engines without symbol support
       if (
         Array.isArray(o) ||
@@ -1133,7 +1129,7 @@ helpers.createForOfIteratorHelper = helper("7.9.0")`
 
     return {
       s: function() {
-        it = o[Symbol.iterator]();
+        it = it.call(o);
       },
       n: function() {
         var step = it.next();
@@ -1159,28 +1155,25 @@ helpers.createForOfIteratorHelperLoose = helper("7.9.0")`
   import unsupportedIterableToArray from "unsupportedIterableToArray";
 
   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) ||
-        (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++] };
-        }
+    var it = typeof Symbol !== "undefined" && o[Symbol.iterator] || o["@@iterator"];
+
+    if (it) return (it = it.call(o)).next.bind(it);
+
+    // Fallback for engines without symbol support
+    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.");
     }
 
-    it = o[Symbol.iterator]();
-    return it.next.bind(it);
+    throw new TypeError("Invalid attempt to iterate non-iterable instance.\\nIn order to be iterable, non-array objects must have a [Symbol.iterator]() method.");
   }
 `;
 

packages/babel-plugin-transform-modules-commonjs/test/fixtures/regression/T7199/output.js

@@ -12,7 +12,7 @@ function _unsupportedIterableToArray(o, minLen) { if (!o) return; if (typeof o =
 
 function _arrayLikeToArray(arr, len) { if (len == null || len > arr.length) len = arr.length; for (var i = 0, arr2 = new Array(len); i < len; i++) arr2[i] = arr[i]; return arr2; }
 
-function _iterableToArrayLimit(arr, i) { if (typeof Symbol === "undefined" || !(Symbol.iterator in Object(arr))) return; var _arr = []; var _n = true; var _d = false; var _e = undefined; try { for (var _i = arr[Symbol.iterator](), _s; !(_n = (_s = _i.next()).done); _n = true) { _arr.push(_s.value); if (i && _arr.length === i) break; } } catch (err) { _d = true; _e = err; } finally { try { if (!_n && _i["return"] != null) _i["return"](); } finally { if (_d) throw _e; } } return _arr; }
+function _iterableToArrayLimit(arr, i) { var _i = arr && (typeof Symbol !== "undefined" && arr[Symbol.iterator] || arr["@@iterator"]); if (_i == null) return; var _arr = []; var _n = true; var _d = false; var _e = undefined; try { for (_i = _i.call(arr), _s; !(_n = (_s = _i.next()).done); _n = true) { _arr.push(_s.value); if (i && _arr.length === i) break; } } catch (err) { _d = true; _e = err; } finally { try { if (!_n && _i["return"] != null) _i["return"](); } finally { if (_d) throw _e; } } return _arr; }
 
 function _arrayWithHoles(arr) { if (Array.isArray(arr)) return arr; }
 

packages/babel-plugin-transform-regenerator/test/fixtures/integration/array-rest/exec.js

@@ -0,0 +1,25 @@
+let iterable = function* fn() {
+  yield 0;
+  yield 1;
+  yield 2;
+}();
+
+let iteratorMethod = iterable[Symbol.iterator];
+iterable[Symbol.iterator] = undefined;
+
+expect(() => {
+  let [_, ...res] = iterable;
+}).toThrow(/non-iterable/);
+
+// In older envs, regenerator uses @@iterator.
+// In those browser Babel must delegate to Array.from, which
+// needs to be polyfilled by the user and support @@iterator.
+iterable["@@iterator"] = iteratorMethod;
+Array.from = (it) => {
+  var i = it["@@iterator"](), arr = [], r;
+  while (!(r = it.next()).done) arr.push(r.value);
+  return arr;
+};
+
+let [_, ...res] = iterable;
+expect(res).toEqual([1, 2]);

packages/babel-plugin-transform-regenerator/test/fixtures/integration/array-rest/options.json

@@ -0,0 +1,3 @@
+{
+  "plugins": ["transform-regenerator", "transform-destructuring"]
+}

packages/babel-plugin-transform-regenerator/test/fixtures/integration/array-spread/exec.js

@@ -0,0 +1,25 @@
+let iterable = function* fn() {
+  yield 1;
+  yield 2;
+}();
+
+let iteratorMethod = iterable[Symbol.iterator];
+iterable[Symbol.iterator] = undefined;
+
+expect(() => {
+  [...iterable];
+}).toThrow(/non-iterable/);
+
+// In older envs, regenerator uses @@iterator.
+// In those browser Babel must delegate to Array.from, which
+// needs to be polyfilled by the user and support @@iterator.
+iterable["@@iterator"] = iteratorMethod;
+Array.from = (it) => {
+  var i = it["@@iterator"](), arr = [], r;
+  while (!(r = it.next()).done) arr.push(r.value);
+  return arr;
+};
+
+let res = [...iterable];
+
+expect(res).toEqual([1, 2]);

packages/babel-plugin-transform-regenerator/test/fixtures/integration/array-spread/options.json

@@ -0,0 +1,3 @@
+{
+  "plugins": ["transform-regenerator", "transform-spread"]
+}

packages/babel-plugin-transform-regenerator/test/fixtures/integration/for-of/exec.js

@@ -0,0 +1,19 @@
+let iterable = function* fn() {
+  yield 1;
+  yield 2;
+}();
+
+let iteratorMethod = iterable[Symbol.iterator];
+iterable[Symbol.iterator] = undefined;
+
+expect(() => {
+  for (let x of iterable);
+}).toThrow(/non-iterable/);
+
+// In older envs, regenerator uses @@iterator.
+iterable["@@iterator"] = iteratorMethod;
+
+let res = [];
+for (let x of iterable) res.push(x);
+
+expect(res).toEqual([1, 2]);

packages/babel-plugin-transform-regenerator/test/fixtures/integration/for-of/options.json

@@ -0,0 +1,3 @@
+{
+  "plugins": ["transform-regenerator", "transform-for-of"]
+}

packages/babel-plugin-transform-spread/test/fixtures/spread/non-iterable/exec.js

@@ -1,6 +1,6 @@
 var o = {};
 
-expect(() => [...undefined]).toThrow(/spread non-iterable/);
+expect(() => [...undefined]).toThrow(/undefined is not iterable|property 'Symbol\(Symbol\.iterator\)' of undefined/);
 
 expect(() => [...o]).toThrow(/spread non-iterable/);
 

packages/babel-preset-env/test/fixtures/corejs2-babel-7/usage-shippedProposals/output.js

@@ -42,7 +42,7 @@ function _wrapAsyncGenerator(fn) { return function () { return new _AsyncGenerat
 
 function _AsyncGenerator(gen) { var front, back; function send(key, arg) { return new Promise(function (resolve, reject) { var request = { key: key, arg: arg, resolve: resolve, reject: reject, next: null }; if (back) { back = back.next = request; } else { front = back = request; resume(key, arg); } }); } function resume(key, arg) { try { var result = gen[key](arg); var value = result.value; var wrappedAwait = value instanceof _AwaitValue; Promise.resolve(wrappedAwait ? value.wrapped : value).then(function (arg) { if (wrappedAwait) { resume(key === "return" ? "return" : "next", arg); return; } settle(result.done ? "return" : "normal", arg); }, function (err) { resume("throw", err); }); } catch (err) { settle("throw", err); } } function settle(type, value) { switch (type) { case "return": front.resolve({ value: value, done: true }); break; case "throw": front.reject(value); break; default: front.resolve({ value: value, done: false }); break; } front = front.next; if (front) { resume(front.key, front.arg); } else { back = null; } } this._invoke = send; if (typeof gen["return"] !== "function") { this["return"] = undefined; } }
 
-if (typeof Symbol === "function" && Symbol.asyncIterator) { _AsyncGenerator.prototype[Symbol.asyncIterator] = function () { return this; }; }
+_AsyncGenerator.prototype[typeof Symbol === "function" && Symbol.asyncIterator || "@@asyncIterator"] = function () { return this; };
 
 _AsyncGenerator.prototype.next = function (arg) { return this._invoke("next", arg); };
 

packages/babel-preset-env/test/fixtures/corejs2/usage-shippedProposals/output.js

@@ -42,7 +42,7 @@ function _wrapAsyncGenerator(fn) { return function () { return new _AsyncGenerat
 
 function _AsyncGenerator(gen) { var front, back; function send(key, arg) { return new Promise(function (resolve, reject) { var request = { key: key, arg: arg, resolve: resolve, reject: reject, next: null }; if (back) { back = back.next = request; } else { front = back = request; resume(key, arg); } }); } function resume(key, arg) { try { var result = gen[key](arg); var value = result.value; var wrappedAwait = value instanceof _AwaitValue; Promise.resolve(wrappedAwait ? value.wrapped : value).then(function (arg) { if (wrappedAwait) { resume(key === "return" ? "return" : "next", arg); return; } settle(result.done ? "return" : "normal", arg); }, function (err) { resume("throw", err); }); } catch (err) { settle("throw", err); } } function settle(type, value) { switch (type) { case "return": front.resolve({ value: value, done: true }); break; case "throw": front.reject(value); break; default: front.resolve({ value: value, done: false }); break; } front = front.next; if (front) { resume(front.key, front.arg); } else { back = null; } } this._invoke = send; if (typeof gen["return"] !== "function") { this["return"] = undefined; } }
 
-if (typeof Symbol === "function" && Symbol.asyncIterator) { _AsyncGenerator.prototype[Symbol.asyncIterator] = function () { return this; }; }
+_AsyncGenerator.prototype[typeof Symbol === "function" && Symbol.asyncIterator || "@@asyncIterator"] = function () { return this; };
 
 _AsyncGenerator.prototype.next = function (arg) { return this._invoke("next", arg); };
 

packages/babel-runtime-corejs2/helpers/esm/iterableToArray.js

@@ -1,6 +1,6 @@
 import _Symbol from "@babel/runtime-corejs2/core-js/symbol";
-import _isIterable from "@babel/runtime-corejs2/core-js/is-iterable";
+import _Symbol$iterator from "@babel/runtime-corejs2/core-js/symbol/iterator";
 import _Array$from from "@babel/runtime-corejs2/core-js/array/from";
 export default function _iterableToArray(iter) {
-  if (typeof _Symbol !== "undefined" && _isIterable(Object(iter))) return _Array$from(iter);
+  if (typeof _Symbol !== "undefined" && iter[_Symbol$iterator] != null || iter["@@iterator"] != null) return _Array$from(iter);
 }

packages/babel-runtime-corejs2/helpers/iterableToArray.js

@@ -1,11 +1,11 @@
 var _Symbol = require("@babel/runtime-corejs2/core-js/symbol");
 
-var _isIterable = require("@babel/runtime-corejs2/core-js/is-iterable");
+var _Symbol$iterator = require("@babel/runtime-corejs2/core-js/symbol/iterator");
 
 var _Array$from = require("@babel/runtime-corejs2/core-js/array/from");
 
 function _iterableToArray(iter) {
-  if (typeof _Symbol !== "undefined" && _isIterable(Object(iter))) return _Array$from(iter);
+  if (typeof _Symbol !== "undefined" && iter[_Symbol$iterator] != null || iter["@@iterator"] != null) return _Array$from(iter);
 }
 
 module.exports = _iterableToArray;

packages/babel-runtime/helpers/esm/iterableToArray.js

@@ -1,3 +1,3 @@
 export default function _iterableToArray(iter) {
-  if (typeof Symbol !== "undefined" && Symbol.iterator in Object(iter)) return Array.from(iter);
+  if (typeof Symbol !== "undefined" && iter[Symbol.iterator] != null || iter["@@iterator"] != null) return Array.from(iter);
 }

packages/babel-runtime/helpers/iterableToArray.js

@@ -1,5 +1,5 @@
 function _iterableToArray(iter) {
-  if (typeof Symbol !== "undefined" && Symbol.iterator in Object(iter)) return Array.from(iter);
+  if (typeof Symbol !== "undefined" && iter[Symbol.iterator] != null || iter["@@iterator"] != null) return Array.from(iter);
 }
 
 module.exports = _iterableToArray;