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