ROT13 decryption implementation in JavaScript

ro13.js

//Created by Jim Morrison, CodingMorrison.com
var alphabet = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz".split("");
var rot13Alphabet = "NOPQRSTUVWXYZABCDEFGHIJKLMnopqrstuvwxyzabcdefghijklm".split("");
var sample = "Lbh qrpelcgrq gur fnzcyr fhpprffshyyl";
var caesar = function(sample) {
	var result = "";
	for (var x=0; x<sample.length; x++) {
		for (var y=0; y<alphabet.length; y++) {
			if (sample[x]==alphabet[y]) {
				result+=rot13Alphabet[y];
			}
		}
		if(sample[x]==" ") {
			result+=" ";
		}
	}
	return result;
}

console.log(caesar(sample));

SW4gb3JkZXIgdG8gZ2VuZXJhdGUgdGhlIGludml0ZSBjb2RlLCBtYWtlIGEgUE9TVCByZXF1ZXN0IHRvIC9hcGkvaW52aXRlL2dlbmVyYXRl