feat(all): add iterator support to Array.from

src/array.js

@@ -1,76 +1,44 @@
 if (!Array.from) {
   Array.from = (function () {
-    var toStr = Object.prototype.toString;
-    var isCallable = function (fn) {
-      return typeof fn === 'function' || toStr.call(fn) === '[object Function]';
+    var toInteger = function(it) {
+      return isNaN(it = +it) ? 0 : (it > 0 ? Math.floor : Math.ceil)(it);
     };
-    var toInteger = function (value) {
-      var number = Number(value);
-      if (isNaN(number)) { return 0; }
-      if (number === 0 || !isFinite(number)) { return number; }
-      return (number > 0 ? 1 : -1) * Math.floor(Math.abs(number));
+    var toLength = function(it) { 
+      return it > 0 ? min(toInteger(it), 0x1fffffffffffff) : 0; // pow(2, 53) - 1 == 9007199254740991 
     };
-    var maxSafeInteger = Math.pow(2, 53) - 1;
-    var toLength = function (value) {
-      var len = toInteger(value);
-      return Math.min(Math.max(len, 0), maxSafeInteger);
+    var iterCall = function(iter, fn, a1, a2) {
+      try {
+        fn(a1, a2);
+      }
+      catch (E) {
+        if (typeof iter.return == 'function') iter.return();
+        throw E;
+      }
     };
 
     // The length property of the from method is 1.
     return function from(arrayLike/*, mapFn, thisArg */) {
-      // 1. Let C be the this value.
-      var C = this;
-
-      // 2. Let items be ToObject(arrayLike).
-      var items = Object(arrayLike);
-
-      // 3. ReturnIfAbrupt(items).
-      if (arrayLike == null) {
-        throw new TypeError("Array.from requires an array-like object - not null or undefined");
-      }
-
-      // 4. If mapfn is undefined, then let mapping be false.
-      var mapFn = arguments.length > 1 ? arguments[1] : void undefined;
-      var T;
-      if (typeof mapFn !== 'undefined') {
-        // 5. else
-        // 5. a If IsCallable(mapfn) is false, throw a TypeError exception.
-        if (!isCallable(mapFn)) {
-          throw new TypeError('Array.from: when provided, the second argument must be a function');
-        }
-
-        // 5. b. If thisArg was supplied, let T be thisArg; else let T be undefined.
-        if (arguments.length > 2) {
-          T = arguments[2];
+      var O = Object(arrayLike)
+        , C = typeof this == 'function' ? this : Array
+        , aLen = arguments.length
+        , mapfn = aLen > 1 ? arguments[1] : undefined
+        , mapping = mapfn !== undefined
+        , index = 0
+        , iterFn = O[Symbol.iterator]
+        , length, result, step, iterator;
+      if (mapping) mapfn = mapfn.bind(aLen > 2 ? arguments[2] : undefined);
+      if (iterFn != undefined && !Array.isArray(arrayLike)) {
+        for (iterator = iterFn.call(O), result = new C; !(step = iterator.next()).done; index++) {
+          result[index] = mapping ? iterCall(mapfn, step.value, index) : step.value;
         }
-      }
-
-      // 10. Let lenValue be Get(items, "length").
-      // 11. Let len be ToLength(lenValue).
-      var len = toLength(items.length);
-
-      // 13. If IsConstructor(C) is true, then
-      // 13. a. Let A be the result of calling the [[Construct]] internal method of C with an argument list containing the single item len.
-      // 14. a. Else, Let A be ArrayCreate(len).
-      var A = isCallable(C) ? Object(new C(len)) : new Array(len);
-
-      // 16. Let k be 0.
-      var k = 0;
-      // 17. Repeat, while k < len… (also steps a - h)
-      var kValue;
-      while (k < len) {
-        kValue = items[k];
-        if (mapFn) {
-          A[k] = typeof T === 'undefined' ? mapFn(kValue, k) : mapFn.call(T, kValue, k);
-        } else {
-          A[k] = kValue;
+      } else {
+        length = toLength(O.length);
+        for (result = new C(length); length > index; index++) {
+          result[index] = mapping ? mapfn(O[index], index) : O[index];
         }
-        k += 1;
       }
-      // 18. Let putStatus be Put(A, "length", len, true).
-      A.length = len;
-      // 20. Return A.
-      return A;
+      result.length = index;
+      return result;
     };
   }());
 }

src/collections.js

@@ -202,6 +202,9 @@ import {PLATFORM} from 'aurelia-pal';
     var p = [0], done = false;
     itp.push(p);
     return {
+      [Symbol.iterator]: function () {
+        return this;
+      },
       next: function() {
         var v, k = p[0];
         if (!done && k < array.length) {