rot.js

var target = "happybirthday";

var r=function(x,r){var s=String,a=Array,b=s.prototype.charCodeAt,c=b.call("a",0);return s.fromCharCode.apply(s,a.prototype.map.call(x,function(v){return c+((b.call(v,0)+r)%26);}))};
for(var i=0;i<26;i++) console.log(r(target, i));