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Simple sets in JavaScript

One of my favourite JavaScript features is its literal object notation. It allows you to declare data structures in JSON, which is a very succinct, C-like syntax. You can use this notation to declare SETs, and the a in b syntax to verify a variable is in a set:

/* Declare your set as a JSON constant */
var valid_widgets = { 
    'widget-viewer': 1,
    'special-viewer': 1,
    'widget-editor': 1 

/* Fail if something isn't in the set */
if ( ! (options.widget in valid_widgets) )
    return false;

/* Profit! */

As the in keyword operates on the index of the referred object, we set the value of the constants to 1 (true). A bit of a hack, but it results in a very clean way of checking if something is part of a set of valid values.