2 var global = require('../internals/global');
3 var bind = require('../internals/function-bind-context');
4 var call = require('../internals/function-call');
5 var toObject = require('../internals/to-object');
6 var callWithSafeIterationClosing = require('../internals/call-with-safe-iteration-closing');
7 var isArrayIteratorMethod = require('../internals/is-array-iterator-method');
8 var isConstructor = require('../internals/is-constructor');
9 var lengthOfArrayLike = require('../internals/length-of-array-like');
10 var createProperty = require('../internals/create-property');
11 var getIterator = require('../internals/get-iterator');
12 var getIteratorMethod = require('../internals/get-iterator-method');
14 var Array = global.Array;
16 // `Array.from` method implementation
17 // https://tc39.es/ecma262/#sec-array.from
18 module.exports = function from(arrayLike /* , mapfn = undefined, thisArg = undefined */) {
19 var O = toObject(arrayLike);
20 var IS_CONSTRUCTOR = isConstructor(this);
21 var argumentsLength = arguments.length;
22 var mapfn = argumentsLength > 1 ? arguments[1] : undefined;
23 var mapping = mapfn !== undefined;
24 if (mapping) mapfn = bind(mapfn, argumentsLength > 2 ? arguments[2] : undefined);
25 var iteratorMethod = getIteratorMethod(O);
27 var length, result, step, iterator, next, value;
28 // if the target is not iterable or it's an array with the default iterator - use a simple case
29 if (iteratorMethod && !(this == Array && isArrayIteratorMethod(iteratorMethod))) {
30 iterator = getIterator(O, iteratorMethod);
32 result = IS_CONSTRUCTOR ? new this() : [];
33 for (;!(step = call(next, iterator)).done; index++) {
34 value = mapping ? callWithSafeIterationClosing(iterator, mapfn, [step.value, index], true) : step.value;
35 createProperty(result, index, value);
38 length = lengthOfArrayLike(O);
39 result = IS_CONSTRUCTOR ? new this(length) : Array(length);
40 for (;length > index; index++) {
41 value = mapping ? mapfn(O[index], index) : O[index];
42 createProperty(result, index, value);
45 result.length = index;