You want to be able to go directly to an entry in an array (especially an array of objects or multidimensional array) without having to loop through the entire array in search of that item.

By taking advantage of the fact that a JavaScript array is a JavaScript object, you can define properties for an array without interfering with the true array portion of the object. Properties can be referenced by name either by string (in parentheses, like array index value) or following a period like a typical object property.

The key to implementing this construction for an existing array is that you must generate a property for each entry with a unique value. If you are implementing this for an array of objects, use a property value that is unique for each entry as the hash table lookup index.