Fast Javascript RFC-compliant UUID generator.

uuidv4.js

    /**
     * Generates an RFC4122-compliant v4 UUID.
     * @returns {string}
     */
    function generateUUID() {
        var timestamp = Date.now(), uuid = '', i = 36, c,
            hexChars = '0123456789abcdef',
            uuidPattern = 'xxxxxxxx-xxxx-4xxx-yxxx-xxxxxxxxxxxx';

        while (i--) {
            c = uuidPattern.charAt(i);
            if (c === 'x') {
                uuid = hexChars.charAt(timestamp + Math.random() * 0xFF & 15)) + uuid;
            } else if (c === '-' || c === '4') {
                uuid = c + uuid;
            } else {
                uuid = hexChars.charAt(Math.random() * 4 + 8 | 0) + uuid;
            }

            timestamp >>= 2;
        }

        return uuid;
    }

Line 13 has a syntax error (parentheses).