create unique id and check duplication.

uniqueId.js

function check() {
    var hash = {},
        key,
        times = Math.pow(10, 9),
        i = 1;

    do {
        key = create3();

        if (hash[key]) {
            console.log('duplicate at the %d times', i);
            return i;
        }
        hash[key] = true;
        if (i % 10000 === 0) {
            console.log('the %d time pass', i);
        }
    }
    while (i++ !== times)
}

function create1() {
    var t = (new Date()).getTime(),
        id = (parseInt(Math.random() * (Math.pow(10, t.toString().length) - 1)) ^ t);
    return Math.abs(id).toString(16);
}

function create2() {
    return Math.random().toString(36).substr(2, 9);
}

function create3() {
    return (((1 + Math.random()) * 0x10000) | 0).toString(16).substring(1);
}
(function () {
    var i = 0,
        times = 20,
        sum = 0;
    do {
        sum += check();
    }
    while (i++ !== times)
    console.log('average deplicate times: %d', sum / times);
})();