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make Object.assign polyfill conditional and spec compliant

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Summary: Replace the non-compliant `Object.assign` with a spec compliant version from Mozilla. Since its spec compliant we can apply conditionally only when a native version is not available.

Reviewed By: yungsters

Differential Revision: D8896359

fbshipit-source-id: 4999fe3094eba2206293bbe28760a4e46cbee6aa
This commit is contained in:
Simon Jensen 2018-08-23 13:51:55 -07:00 committed by Facebook Github Bot
parent 1329d18c6a
commit 966bb63a80
1 changed files with 23 additions and 49 deletions
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72
Libraries/polyfills/Object.es6.js
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@ -6,60 +6,34 @@
*
* @format
* @polyfill
* @nolint
*/
// WARNING: This is an optimized version that fails on hasOwnProperty checks
// and non objects. It's not spec-compliant. It's a perf optimization.
// This is only needed for iOS 8 and current Android JSC.
// https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/assign
Object.assign = function(target, sources) {
if (__DEV__) {
if (target == null) {
throw new TypeError('Object.assign target cannot be null or undefined');
}
if (typeof target !== 'object' && typeof target !== 'function') {
throw new TypeError(
'In this environment the target of assign MUST be an object. ' +
'This error is a performance optimization and not spec compliant.',
);
}
}
for (var nextIndex = 1; nextIndex < arguments.length; nextIndex++) {
var nextSource = arguments[nextIndex];
if (nextSource == null) {
continue;
}
if (__DEV__) {
if (typeof nextSource !== 'object' && typeof nextSource !== 'function') {
throw new TypeError(
'In this environment the sources for assign MUST be an object. ' +
'This error is a performance optimization and not spec compliant.',
);
if (typeof Object.assign !== 'function') {
Object.defineProperty(Object, 'assign', {
value: function assign(target, varArgs) {
'use strict';
if (target == null) {
throw new TypeError('Cannot convert undefined or null to object');
}
}
// We don't currently support accessors nor proxies. Therefore this
// copy cannot throw. If we ever supported this then we must handle
// exceptions and side-effects.
let to = Object(target);
for (var key in nextSource) {
if (__DEV__) {
var hasOwnProperty = Object.prototype.hasOwnProperty;
if (!hasOwnProperty.call(nextSource, key)) {
throw new TypeError(
'One of the sources for assign has an enumerable key on the ' +
'prototype chain. Are you trying to assign a prototype property? ' +
"We don't allow it, as this is an edge case that we do not support. " +
'This error is a performance optimization and not spec compliant.',
);
for (let index = 1; index < arguments.length; index++) {
let nextSource = arguments[index];
if (nextSource != null) {
for (let nextKey in nextSource) {
if (Object.prototype.hasOwnProperty.call(nextSource, nextKey)) {
to[nextKey] = nextSource[nextKey];
}
}
}
}
target[key] = nextSource[key];
}
}
return target;
};
return to;
},
writable: true,
configurable: true,
});
}