js generates several methods of UUID

Introduction:

UUID (Universally Unique IDentifier) Universally unique identifier.
A UUID is an algorithmically generated numerical identifier with a binary length of 128 bits. UUID
format is "xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx" where x is 0-9 or af
A 32-bit hexadecimal number in the range. In an ideal world, no computer or cluster of computers will generate two identical UUIDs.

1. The first

 function guid() {
    return 'xxxxxxxx-xxxx-4xxx-yxxx-xxxxxxxxxxxx'.replace(/[xy]/g, function (c) {
        var r = Math.random() * 16 | 0,
            v = c == 'x' ? r : (r & 0x3 | 0x8);
        return v.toString(16);
    });
}
guid() // "a1ca0f7b-51bd-4bf3-a5d5-6a74f6adc1c7"

2. The second

 function uuid() {
    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] = "-";

    var uuid = s.join("");
    return uuid;
}
uuid() // "ffb7cefd-02cb-4853-8238-c0292cf988d5"

3. The third

 function guid2() {
    function S4() {
        return (((1 + Math.random()) * 0x10000) | 0).toString(16).substring(1);
    }
    return (S4() + S4() + "-" + S4() + "-" + S4() + "-" + S4() + "-" + S4() + S4() + S4());
}
guid2() // "748eea29-f842-4af9-a552-e1e1aa3ed979"

4. The fourth

 // 指定长度和基数
function uuid2(len, radix) {
    var chars = '0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz'.split('');
    var uuid = [],
        i;
    radix = radix || chars.length;

    if (len) {
        // Compact form
        for (i = 0; i < len; i++) uuid[i] = chars[0 | Math.random() * radix];
    } else {
        // rfc4122, version 4 form
        var r;

        // rfc4122 requires these characters
        uuid[8] = uuid[13] = uuid[18] = uuid[23] = '-';
        uuid[14] = '4';

        // Fill in random data.  At i==19 set the high bits of clock sequence as
        // per rfc4122, sec. 4.1.5
        for (i = 0; i < 36; i++) {
            if (!uuid[i]) {
                r = 0 | Math.random() * 16;
                uuid[i] = chars[(i == 19) ? (r & 0x3) | 0x8 : r];
            }
        }
    }

    return uuid.join('');
}
uuid2(16, 16) // "277571702EE33E11"

5. Fifth description: Generate 32-bit UUID method

 function uuid() {
    var s = [];
    var hexDigits = "0123456789abcdef";
    for (var i = 0; i < 32; 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];
    var uuid = s.join("");
    return uuid;
}