Created
May 10, 2016 05:01
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Set a unique id property _uid on all objects.
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| // Generates a unique, read-only id for any object. This modifies Object.prototype, | |
| // so should only be used for testing, within a limited scope. | |
| // The _uid is generated for an object the first time it's accessed. | |
| (function() { | |
| var id = 0; | |
| Object.defineProperty(Object.prototype, '_uid', { | |
| // The prototype getter sets up a property on the instance. Because | |
| // the new instance-prop masks this one, we know this will only ever | |
| // be called at most once for any given object. | |
| get: function () { | |
| Object.defineProperty(this, '_uid', { | |
| value: id++, | |
| writable: false, | |
| enumerable: false, | |
| }); | |
| return this._uid; | |
| }, | |
| enumerable: false, | |
| }); | |
| })(); | |
| function assert(p) { if (!p) throw Error('Not!'); } | |
| var obj = {}; | |
| assert(obj._uid == 0); | |
| assert({}._uid == 1); | |
| assert([]._uid == 2); | |
| assert(obj._uid == 0); // still |
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