Create Enums in Javascript (immutable dictionaries of string:int pairings).

enum.js

/* global define */
/**
 * Enums in Javascript
 *
 * Makes an immutable dictionary with string:int pairings to emulate Enums.
 * Usage example: Colours = Enum('RED', 'GREEN', 'BLUE');
 *
 * @author Gideon Farrell <me@gideonfarrell.co.uk>
 * 
 */
define(function() {
    'use strict';

    var Enum = function() {
        var e     = {},  // the enumerator object
            args  = Array.prototype.slice.apply(arguments),
            count = args.length;

        // Iterate over the args, and add them as enum keys
        var index = 1;
        for(var i = 0; i < count; i++) {
            var key = args[i];
            if(e.hasOwnProperty(key)) {
                continue;
            } else {
                if(typeof Object.defineProperty == 'function') {
                    // Javascript 1.8.5, use defineProperty
                    Object.defineProperty(e, key, {configurable: false, enumerable: true, value: index, writable: false});
                } else if(typeof e.__defineGetter__ == 'function' && typeof e.__defineSetter__ == 'function') {
                    // This is non-standard, but we'll use it if defineProperty fails
                    // (it has to be present though)
                    e.__defineGetter__(key, function() { return index; });
                    e.__defineSetter__(key, function() { return false; });
                } else {
                    // if all else fails, it won't be immutable, but we'll be graceful about it
                    e[key] = index;
                }
                index++;
            }
        }

        return e;
    };

    return Enum;
});