randomString (length) {
        length = length || 6;

        var result = [],
            i;

        for (i = 0; i < length; i++) {
            result[i] = ASCII_SOURCE[(Math.random() * ASCII_SOURCE_LENGTH) | 0];
        }

        return result.join(EMPTY);
    }
Generates a random string of given length (useful for nonce generation, etc).

@param {Number} length -