JavaScript function to generate a pseudo random GUID.

/**
 * Generates a pseudo random GUID (globally unique identifier).
 *
 * @return {string}
 */
function guid() {
    var id = "",
        i,
        random;

    for (i = 0; i < 32; i++) {
        random = (math.random() * 16) | 0;

        if (i == 8 || i == 12 || i == 16 || i == 20) {
            id += "-";
        }

        id += (i == 12 ? 4 : i == 16 ? (random & 3) | 8 : random).toString(16);
    }

    return id;
}