Looking for "Good Enough" client-side UUID generator

uuid.js

/*
    I cannot claim this - it was recommended by a friend as a 'good enough' unique id generator
    for local client side scenarios in the browser.  The use case I'm looking to address has to
    do with cross-frame messaging, where each point of origin needs a unique id (to be used as an 
    "origin" or correlation identifier).  Therefore - the IDs do not need to be unique on a large
    scale (e.g. - across a vast network of connected clients), but only in the browser, locally,
    for the life of the session.  Question is: is this good enough?
*/
function createUUID() {
    var s = [];
    var hexDigits = "0123456789abcdef";
    for (var i = 0; i < 36; i++) {
        s[i] = hexDigits.substr(Math.floor(Math.random() * 0x10), 1);
    }
    s[14] = "4";  // bits 12-15 of the time_hi_and_version field to 0010
    s[19] = hexDigits.substr((s[19] & 0x3) | 0x8, 1);  // bits 6-7 of the clock_seq_hi_and_reserved to 01
    s[8] = s[13] = s[18] = s[23] = "-";
    return s.join("");
}

UUID strong enough for client applications, not for scale.