56 lines
1.3 KiB
JavaScript
56 lines
1.3 KiB
JavaScript
|
'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;
|
||
|
|
};
|