56 lines
1.3 KiB
JavaScript
56 lines
1.3 KiB
JavaScript
'use strict';
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var implementation = require('./implementation');
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var lacksProperEnumerationOrder = function () {
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if (!Object.assign) {
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return false;
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}
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/*
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* v8, specifically in node 4.x, has a bug with incorrect property enumeration order
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* note: this does not detect the bug unless there's 20 characters
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*/
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var str = 'abcdefghijklmnopqrst';
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var letters = str.split('');
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var map = {};
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for (var i = 0; i < letters.length; ++i) {
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map[letters[i]] = letters[i];
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}
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var obj = Object.assign({}, map);
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var actual = '';
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for (var k in obj) {
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actual += k;
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}
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return str !== actual;
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};
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var assignHasPendingExceptions = function () {
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if (!Object.assign || !Object.preventExtensions) {
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return false;
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}
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/*
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* Firefox 37 still has "pending exception" logic in its Object.assign implementation,
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* which is 72% slower than our shim, and Firefox 40's native implementation.
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*/
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var thrower = Object.preventExtensions({ 1: 2 });
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try {
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Object.assign(thrower, 'xy');
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} catch (e) {
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return thrower[1] === 'y';
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}
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return false;
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};
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module.exports = function getPolyfill() {
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if (!Object.assign) {
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return implementation;
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}
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if (lacksProperEnumerationOrder()) {
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return implementation;
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}
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if (assignHasPendingExceptions()) {
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return implementation;
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}
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return Object.assign;
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};
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