Polyfill Array.from

Reviewed By: cpojer

Differential Revision: D2627437

fb-gh-sync-id: 6a7c94e13db772d96cbd8ebab37eccb0826963bc

packager/react-packager/src/Resolver/polyfills/Array.prototype.es6.js

@@ -55,4 +55,78 @@
       }
     });
   }
+
+  /**
+   * Creates an array from array like objects.
+   *
+   * https://people.mozilla.org/~jorendorff/es6-draft.html#sec-array.from
+   */
+  if (!Array.from) {
+    Array.from = function(arrayLike /*, mapFn, thisArg */) {
+      if (arrayLike == null) {
+        throw new TypeError('Object is null or undefined');
+      }
+
+      // Optional args.
+      var mapFn = arguments[1];
+      var thisArg = arguments[2];
+
+      var C = this;
+      var items = Object(arrayLike);
+      var symbolIterator = typeof Symbol === 'function'
+        ? Symbol.iterator
+        : '@@iterator';
+      var mapping = typeof mapFn === 'function';
+      var usingIterator = typeof items[symbolIterator] === 'function';
+      var key = 0;
+      var ret;
+      var value;
+
+      if (usingIterator) {
+        ret = typeof C === 'function'
+          ? new C()
+          : [];
+        var it = items[symbolIterator]();
+        var next;
+
+        while (!(next = it.next()).done) {
+          value = next.value;
+
+          if (mapping) {
+            value = mapFn.call(thisArg, value, key);
+          }
+
+          ret[key] = value;
+          key += 1;
+        }
+
+        ret.length = key;
+        return ret;
+      }
+
+      var len = items.length;
+      if (isNaN(len) || len < 0) {
+        len = 0;
+      }
+
+      ret = typeof C === 'function'
+        ? new C(len)
+        : new Array(len);
+
+      while (key < len) {
+        value = items[key];
+
+        if (mapping) {
+          value = mapFn.call(thisArg, value, key);
+        }
+
+        ret[key] = value;
+
+        key += 1;
+      }
+
+      ret.length = key;
+      return ret;
+    };
+  }
 })();