### <a href="Function_evisit_core_js_data_toLookup.md#function-toLookup"></a>function toLookup(key, data)
> #### Parameters
>  * **key** 
>    * (<i>String</i>) Key to match on all objects. If key is undefined or null, the index will be used instead.
>  * **data** 
>    * (<i>Array</i>) Array to create map from
> 
> #### Return value
> * (<i>Object</i>) Each key in the object will be the value in the Array specified by 'key'
> 
> #### Description
> This takes an Array and returns a reference map for quick lookup.
> 
> #### See Also
>  * <a href="Function_evisit_core_js_data_toLookup.md#function-extract">evisit-core-js.data.extract</a>
> 
> #### Examples
>  ```javascript
> var myMap = toLookup('id', [
>  {
>    id:'derp',
>    field: 'derp'
>  },
>  {
>    id:'dog',
>    field: 'dog'
>  },
>  {
>    id:'cat',
>    field: 'cat'
>  }
> ]);
> myMap === {
>  'derp': {
>    id:'derp',
>    field: 'derp'
>  },
>  'dog': {
>    id:'dog',
>    field: 'dog'
>  },
>  'cat': {
>    id:'cat',
>    field: 'cat'
>  }
> };
>  ```
> 
> 
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