Base64 for JS (safe for IDs)

b64.js

/*
Base64.encode(str):
	Returns a string that is guaranteed to be a valid ID and can be decoded into its
	original form. No two inputs generate the same output.
Base64.decode(str):
	Returns the original string from the output of Base64.encode.
 */
var Base64 = {
	characters: "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-_.",
	'encode': function(data) {
		if (!data) {
			return data;
		}
		var o1, o2, o3, h1, h2, h3, h4, bits, r, i = 0, ac = 0, enc = '', tmp = [];
		do {
			o1 = data.charCodeAt(i++);
			o2 = data.charCodeAt(i++);
			o3 = data.charCodeAt(i++);
			bits = o1 << 16 | o2 << 8 | o3;
			h1 = bits >> 18 & 0x3f;
			h2 = bits >> 12 & 0x3f;
			h3 = bits >> 6 & 0x3f;
			h4 = bits & 0x3f;
			tmp[ac++] = Base64.characters.charAt(h1) + Base64.characters.charAt(h2) + Base64.characters.charAt(h3) + Base64.characters.charAt(h4);
		} while (i < data.length);
		enc = tmp.join('');
		r = data.length % 3;
		return 'b' + (r ? enc.slice(0, r - 3) : enc) + '...'.slice(r || 3);
	},
	'decode': function(data){
		if (!data) {
			return data;
		}
		var o1, o2, o3, h1, h2, h3, h4, bits, i = 0, ac = 0, tmp = [];
		data = data.substr(1);
		do {
			h1 = Base64.characters.indexOf(data.charAt(i++));
			h2 = Base64.characters.indexOf(data.charAt(i++));
			h3 = Base64.characters.indexOf(data.charAt(i++));
			h4 = Base64.characters.indexOf(data.charAt(i++));
			bits = h1 << 18 | h2 << 12 | h3 << 6 | h4;
			o1 = bits >> 16 & 0xff;
			o2 = bits >> 8 & 0xff;
			o3 = bits & 0xff;
			if (h3 == 64) {
				tmp[ac++] = String.fromCharCode(o1);
			} else if (h4 == 64) {
				tmp[ac++] = String.fromCharCode(o1, o2);
			} else {
				tmp[ac++] = String.fromCharCode(o1, o2, o3);
			}
		} while (i < data.length);
		return tmp.join('');
	}
};

b64.min.js

var g={a:"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-_.",encode:function(a){if(!a)return a;var b,e,c,d,h=0,i=0,f="",f=[];do b=a.charCodeAt(h++),e=a.charCodeAt(h++),c=a.charCodeAt(h++),d=b<<16|e<<8|c,b=d>>18&63,e=d>>12&63,c=d>>6&63,d&=63,f[i++]=g.a.charAt(b)+g.a.charAt(e)+g.a.charAt(c)+g.a.charAt(d);while(h<a.length);f=f.join("");a=a.length%3;return"b"+(a?f.slice(0,a-3):f)+"...".slice(a||3)},decode:function(a){if(!a)return a;var b,e,c,d,h,i=0,f=0,j=[],a=a.substr(1);do b=g.a.indexOf(a.charAt(i++)),
e=g.a.indexOf(a.charAt(i++)),d=g.a.indexOf(a.charAt(i++)),h=g.a.indexOf(a.charAt(i++)),c=b<<18|e<<12|d<<6|h,b=c>>16&255,e=c>>8&255,c&=255,64==d?j[f++]=String.fromCharCode(b):64==h?j[f++]=String.fromCharCode(b,e):j[f++]=String.fromCharCode(b,e,c);while(i<a.length);return j.join("")}};window.Base64=g;

example.js

var encoded = Base64.encode('hello world!!');
console.log(encoded); // "baGVsbG8gd29ybGQhIQ.."
var decoded = Base64.decode(encoded);
console.log(decoded); // "hello world!!"