UUID JS generator based on http://gotochriswest.com/blog/2012/03/26/javascript-guid-uuid-generator/

uuid.js

var UUID = function() {
  // The object literal used to keep track of all of the generated IDs.
  this.used = {};
};

// The globally visible function which is used to generate
// UUID that are unique for the remainder of the page session.
UUID.prototype.generate = function(id) {
  for(;this.used[id = this.randomHex(8) + "-" + this.randomHex(4) + "-"
            + this.randomHex(4) + "-" + this.randomHex(4) + this.randomHex(8)];){}
  this.used[id] = 1;
  return id;
}

// Used to generate a hex number which is padded by zeros to
// display the specified amount of digits.  The param passed
// probably shouldn't be more than 8.
UUID.prototype.randomHex = function(len) {
  return (new Array(len).join(0)
            + parseInt(Math.pow(2, len * 4) * Math.random()
          ).toString(16)).slice(-len);
}