Base64

Browser:

String.prototype.base64Decode = function() { return atob(this) }
String.prototype.base64Encode = function() { return btoa(this) }

Node.js

Array.prototype.base64Encode = function() { return new Buffer(this.slice()).toString('base64'); }
String.prototype.base64Decode = function() { return Array.prototype.slice.apply(new Buffer(this.toString(), 'base64')); }

Hex encoding

String.prototype.hexDecode = function() { return this.match(/../g).map(function(c) { return parseInt(c, 16) }) }
String.prototype.hexEncode = function() { return this.toByteArray().hexEncode() }
Number.prototype.toHex = function() { return ("0" + this.toString(16)).substr(-2) }
Array.prototype.hexEncode = function() { return this.map(function(x) { return x.toHex() }).join("") }

Ascii string vs byte array

String.prototype.toByte = function() { return this.charCodeAt(0) }
Number.prototype.toChar = function() { return String.fromCharCode(this) }
String.prototype.toByteArray = function() { return this.split('').map(function(c){ return c.toByte() }) }
Array.prototype.asString = function() { return String.fromCharCode.apply(null, this) }

Xor and random bytes

Array.prototype.xor = function(ar) { return this.map(function(e, i) { return e ^ ar[i % ar.length]; }) }
Array.randomBytes = function(length) { return Array.prototype.slice.call(crypto.getRandomValues(new Uint8Array(length))) }

Testing for insecure direct object references with jQuery

var exists= []; for(var i = 0; i < 100 ; i++) (function(x) { $.getJSON("/?id=" + x).success(function() { e.push(x) }) })(i);

Examples

XOR plain text with random key

var key = Array.randomBytes(16);
var cipher = "Hello world".toByteArray().xor(key).hexEncode();