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