28 lines
1.1 KiB
JavaScript
28 lines
1.1 KiB
JavaScript
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'use strict';
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var aFunction = require('../internals/a-function');
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var isObject = require('../internals/is-object');
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var slice = [].slice;
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var factories = {};
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var construct = function (C, argsLength, args) {
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if (!(argsLength in factories)) {
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for (var list = [], i = 0; i < argsLength; i++) list[i] = 'a[' + i + ']';
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// eslint-disable-next-line no-new-func -- we have no proper alternatives, IE8- only
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factories[argsLength] = Function('C,a', 'return new C(' + list.join(',') + ')');
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} return factories[argsLength](C, args);
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};
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// `Function.prototype.bind` method implementation
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// https://tc39.es/ecma262/#sec-function.prototype.bind
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module.exports = Function.bind || function bind(that /* , ...args */) {
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var fn = aFunction(this);
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var partArgs = slice.call(arguments, 1);
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var boundFunction = function bound(/* args... */) {
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var args = partArgs.concat(slice.call(arguments));
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return this instanceof boundFunction ? construct(fn, args.length, args) : fn.apply(that, args);
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};
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if (isObject(fn.prototype)) boundFunction.prototype = fn.prototype;
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return boundFunction;
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};
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