Rot13 static JavaScript class

Rot13.js

/**
 * Rot13 class.
 * @author Christoffer Niska <christoffer.niska@nordsoftware.com>
 * @copyright Copyright (c) 2011, Christoffer Niska
 * @license  http://www.opensource.org/licenses/bsd-license.php New BSD License
 */
var Rot13 = {
	map: null,
	length: 0,
	init: function() {
		if (this.map)
			return;

		var i, map = [],
			chars = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz',
			length = chars.length;

		for (i = 0; i < length; ++i) {
			map.push(chars.charAt((i + 13) % length));
		}

		this.map = map;
		this.length = length;
	},
	decode: function(text) {
		this.init();

		var i, c, idx, result = '';

		for (i = 0; i < text.length; ++i) {
			c = text.charAt(i);
			idx = (this.map.indexOf(c) - 13) % this.length;

			if (idx < 13 && idx >= 0 ) {
				idx += this.length / 2;
			}

			result += this.map[idx] ? this.map[idx] : c;
		}

		return result;
	}
};

I use this class to decode email addresses client side that are encoded using Rot13 on the server side to prevent them from being collected by spambots.