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    <p>If you have a really huge object, you could use a nice <a href="https://github.com/Benvie/WeakMap" rel="nofollow">weakmap implementation</a> <em>with the complexity of O(1)</em> to store keys per single object. Therefor you have to implement your hash collection, so when setting a key-value pair, you also store the key in the weakmap. I made also some bench. comparison of this custom HashMap vs RawObject search - <a href="http://jsperf.com/store-keys-in-weakmap-vs-continues-search" rel="nofollow">jsperf</a></p> <pre><code>function HashMap() { this.__map = new WeakMap; this.__hash = {}; } HashMap.prototype = { set: function(key, value){ this.unset(key); if (value == null) return; this.__hash[key] = value; var keys = this.__map.get(value); if (keys == null) this.__map.set(value, keys = []); keys.push(key); }, unset: function(key){ var value = this.__hash[key]; if (value) { var keys = this.__map.get(value), index = keys.indexOf(key); keys.splice(index, 1); } this.__hash[key] = void 0; }, get: function(key){ return this.__hash[key]; }, getKeys: function(value){ return this.__map.get(value); } }; </code></pre> <p>WeakMap uses <code>Object.defineProperty</code> method in its core. For this reason there are some limitations:</p> <ul> <li>browsers: IE9+</li> <li>Objects as Values in above HashMap example, because they are used as Keys in WeakMap Collection</li> </ul> <p>But this approach makes a huge performance boost, as there is no need to iterate over the object, to look for a specific value. </p>
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    1. POReferencing index of an Object within an Object using something equivelant Object.indexOf
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    1. COSuper interesting! I am a bit unclear about how this works. When I try to use it in my scenario it appears that one can't use Strings as a Keys? Upon further digging, it seems you are only allowed to use Objects as keys? I wonder if this would work with Functions as values...
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      1. USArjun Mehta
    2. COYes, from the example above you cannt use primitives, _like strings, numbers_ in **Values**, but Objects and **Functions** can - this is the weakmap limitation. But you can convert any string to an object- `str = new String(str)`. This works very simple - we use WeakMap shim - this is a collection where we can have objects and functions as Keys. So we store data in two collections: `property:value`(String:Object/Function) and `value: properties`(Object/Function:Array<String>). So we have much better performance, when we need to get all keys for a value - O(1) instead of O(n)
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    3. COI just tried this and it works really well! Could you please update your answer to include the limitations and further explanation of how to use this method. Then I will select it as it seems to be a really efficient way.
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