UUID (GUID) generation

guid-builder.js

/**
 * Returns unique GUID on every call as per pseudo-number RFC4122 standards.
 *
 * @type {function}
 * @returns {string}
 */
module.exports = (function() {
    var E = '',
        H = '-',

        rnd = (window || global).Math.random;

    return function() {
        var n, r; // r = result , n = numeric variable for positional checks

        // if "n" is not 9 or 14 or 19 or 24 return a random number or 4
        // if "n" is not 15 genetate a random number from 0 to 15
        // `(n ^ 20 ? 16 : 4)` := unless "n" is 20, in which case a random number from 8 to 11 otherwise 4
        // 
        // in other cases (if "n" is 9,14,19,24) insert "-"
        for (r = n = E; n++ < 36; r += n * 51 & 52 ? (n ^ 15 ? 8 ^ rnd() * (n ^ 20 ? 16 : 4) : 4).toString(16) : H);
        return r;
    }
}());

guid-replacer.js

/**
 * Returns unique GUID on every call as per pseudo-number RFC4122 standards.
 *
 * @type {function}
 * @returns {string}
 *
 * @note Uses string replacement to build the ID.
 */
module.exports = (function() {
    var MASK = 'xxxxxxxx-xxxx-4xxx-yxxx-xxxxxxxxxxxx',
        SX = 'x',

        base = 16,
        rnd = Math.random,
        flr = Math.floor,
        now = Date.now;

    return function() {
        var d = now();
        return (MASK.replace(/[xy]/g, function(c) {
            var r = (d + rnd() * base) % base | 0;
            d = flr(d / base);
            return (c === SX ? r : (r & 0x7 | 0x8)).toString(base);
        }));
    }
}());