generate a unique UUID using Javascript Math.random

generateUniqueId.js

// from alexmorleyfinch's comment on this thread:
// https://gist.github.com/gordonbrander/2230317#gistcomment-1618310
var generateUniqueId = function(){
    function chr4(){
        return Math.random().toString(16).slice(-4);
    };
    return chr4() + chr4() +
        '-' + chr4() +
        '-' + chr4() +
        '-' + chr4() +
        '-' + chr4() + chr4() + chr4();
};