Add for-of fallback for arrays in browsers without symbol supp… (#11263)

* Add for-of fallback for arrays in browsers without symbol support

* Update after rebase

* Re-throw error when iterating array

* Update fixture

packages/babel-helpers/src/helpers.js

@@ -1078,8 +1078,24 @@ helpers.createForOfIteratorHelper = helper("7.9.0")`
   // f: finish (always called at the end)
 
   export default function _createForOfIteratorHelper(o) {
-    if (typeof Symbol === "undefined" || o[Symbol.iterator] == null)
+    if (typeof Symbol === "undefined" || o[Symbol.iterator] == null) {
+      // Fallback for engines without symbol support
+      if (Array.isArray(o)) {
+        var i = 0;
+        var F = function(){};
+        return {
+          s: F,
+          n: function() {
+            if (i >= o.length) return { done: true };
+            return { done: false, value: o[i++] };
+          },
+          e: function(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;
 
@@ -1112,6 +1128,7 @@ helpers.createForOfIteratorHelperLoose = helper("7.9.0")`
     var i = 0;
 
     if (typeof Symbol === "undefined" || o[Symbol.iterator] == null) {
+      // Fallback for engines without symbol support
       if (Array.isArray(o))
         return function() {
           if (i >= o.length) return { done: true };

packages/babel-plugin-transform-for-of/test/fixtures/spec-exec/array-symbol-unsupported-throw.js

@@ -0,0 +1,23 @@
+var a = (() => [1, 2, 3])();
+
+// Simulate old environment
+let _Symbol = Symbol;
+Symbol = void 0;
+try {
+  let didErr = false, err;
+  let obj = {};
+
+  try {
+    for (let i of a) {
+      if (i === 2) throw obj;
+    }
+  } catch (e) {
+    didErr = true;
+    err = e;
+  }
+
+  expect(didErr).toBe(true);
+  expect(obj).toBe(err);
+} finally {
+  Symbol = _Symbol;
+}

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

@@ -10,7 +10,7 @@ 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) 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(_e) { didErr = true; err = _e; }, f: function f() { try { if (!normalCompletion && it["return"] != null) it["return"](); } finally { if (didErr) throw err; } } }; }
+function _createForOfIteratorHelper(o) { if (typeof Symbol === "undefined" || o[Symbol.iterator] == null) { if (Array.isArray(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; } } }; }
 
 // https://github.com/babel/babel/issues/7557
 var _iterator = _createForOfIteratorHelper(c),