UID Generating in JavaScript

gen_uid.js

// 还需要了解的：
//  - 什么是 UID
//  - 这四种方式优劣

function getId() {
    return "xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx".replace(/x/g, function() {
        return Math.floor(Math.random()*16).toString(16).toUpperCase();
    });
}

function generateGuid() {
    var result, i, j;
    result = '';
    for(j=0; j<32; j++) {
        if( j == 8 || j == 12|| j == 16|| j == 20)
            result = result + '-';
        i = Math.floor(Math.random()*16).toString(16).toUpperCase();
        result = result + i;
    }
    return result;
}

// http://stackoverflow.com/questions/3242324/javascript-dateobj-gettime-for-a-uid-is-the-length-not-fixed
Math.random().toString(36).substr(2,9)

// http://stackoverflow.com/questions/6248666/how-to-generate-short-uid-like-ax4j9z-in-js
function generateUIDNotMoreThan1million() {
    return ("0000" + (Math.random()*Math.pow(36,4) << 0).toString(36)).substr(-4)
}

If you replace the String "xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx" with "xxxxxxxx-xxxx-4xxx-xxxx-xxxxxxxxxxxx" it should be standard conform.