Provides an immutable enum type

Enum.js

/**
 * Enum.js
 * Provides an immutable Enum type
 * Copyright (c) 2014 marlun78
 * MIT License, https://gist.github.com/marlun78/bd0800cf5e8053ba9f83
 * 
 * @example:
 * var colors = new Enum({
 *     RED: '#f00',
 *     GREEN: '#0f0',
 *     BLUE: '#00f'
 * });
 * 
 * colors.RED;                   // #f00
 * 
 * colors.getValueByKey('RED');  // #f00
 * colors.getValueByKey('dog');  // undefined
 *
 * colors.hasValue('#00f');      // true
 * colors.hasValue('dog');       // false
 *
 * colors.getKeyByValue('#f00'); // 'RED'
 * colors.getKeyByValue('dog');  // undefined
 *
 * colors.hasKey('BLUE');        // true
 * colors.hasKey('dog');         // false
 * 
 * colors.dog = 'pudel';         // 'pudel'
 * colors.hasKey('dog');         // false
 * colors.dog;                   // undefined
 */
var Enum = (function () {

    'use strict';
    
    /**
     * Immutable Enum Type
     * @typedef {Object} Enum
     * @property {Function} getKeys
     * @property {Function} getValues
     * @property {Function} hasKeys
     * @property {Function} hasValues
     */

    /**
     * @constructor
     * @param {object} map
     * @returns {enum}
     */
    function Enum(map) {
        // Copy properties from host map
        for (var key in map) {
            if (map.hasOwnProperty(key)) this[key] = map[key];
        }
        // Make immutable
        Object.freeze(this);
    }

    Enum.prototype = {
        constructor: Enum,
        /**
         * Retrieves the key for a value
         * @param {*} value - The value of the key to get
         * @returns {string|undefined}
         */
        getKeyByValue: function getKeyByValue(value) {
            for (var key in this) {
                if (this.hasOwnProperty(key) && this[key] === value) return key;
            }
        },
        /**
         * Retrieves the value for a key
         * @param {string} key - The key of the value to get
         * @returns {*}
         */
        getValueByKey: function getValueByKey(key) {
            if (this.hasOwnProperty(key)) return this[key];
        },
        /**
         * Checks if the passed key exists or not
         * @param {string} key - The key of the value to get
         * @returns {Boolean}
         */
        hasKey: function hasKey(key) {
            return this.hasOwnProperty(key);
        },
        /**
         * Checks if the passed value exists or not
         * @param {*} value - The value of the key to get
         * @returns {boolean}
         */
        hasValue: function hasValue(value) {
            for (var key in this) {
                if (this.hasOwnProperty(key) && this[key] === value) return true;
            }
            return false;
        }
    };

    return Enum;

}());