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- 'use strict';
- var bind = require('../internals/function-bind-context');
- var call = require('../internals/function-call');
- var toObject = require('../internals/to-object');
- var callWithSafeIterationClosing = require('../internals/call-with-safe-iteration-closing');
- var isArrayIteratorMethod = require('../internals/is-array-iterator-method');
- var isConstructor = require('../internals/is-constructor');
- var lengthOfArrayLike = require('../internals/length-of-array-like');
- var createProperty = require('../internals/create-property');
- var getIterator = require('../internals/get-iterator');
- var getIteratorMethod = require('../internals/get-iterator-method');
-
- var $Array = Array;
-
- // `Array.from` method implementation
- // https://tc39.es/ecma262/#sec-array.from
- module.exports = function from(arrayLike /* , mapfn = undefined, thisArg = undefined */) {
- var O = toObject(arrayLike);
- var IS_CONSTRUCTOR = isConstructor(this);
- var argumentsLength = arguments.length;
- var mapfn = argumentsLength > 1 ? arguments[1] : undefined;
- var mapping = mapfn !== undefined;
- if (mapping) mapfn = bind(mapfn, argumentsLength > 2 ? arguments[2] : undefined);
- var iteratorMethod = getIteratorMethod(O);
- var index = 0;
- var length, result, step, iterator, next, value;
- // if the target is not iterable or it's an array with the default iterator - use a simple case
- if (iteratorMethod && !(this === $Array && isArrayIteratorMethod(iteratorMethod))) {
- result = IS_CONSTRUCTOR ? new this() : [];
- iterator = getIterator(O, iteratorMethod);
- next = iterator.next;
- for (;!(step = call(next, iterator)).done; index++) {
- value = mapping ? callWithSafeIterationClosing(iterator, mapfn, [step.value, index], true) : step.value;
- createProperty(result, index, value);
- }
- } else {
- length = lengthOfArrayLike(O);
- result = IS_CONSTRUCTOR ? new this(length) : $Array(length);
- for (;length > index; index++) {
- value = mapping ? mapfn(O[index], index) : O[index];
- createProperty(result, index, value);
- }
- }
- result.length = index;
- return result;
- };
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