UUID(Universally Unique Identifier) 是長為 128 bits 的通用唯一識別碼，它由 RFC 4122 定義，最早被用于阿波羅網(wǎng)絡(luò)計算系統(tǒng)(Apollo Network Computing System) 和微軟的 Windows 平臺，如今 OpenStack 也廣泛的使用它來標(biāo)志計算、存儲和網(wǎng)絡(luò)等資源。UUID 的目的，是讓分布式系統(tǒng)中的所有元素，都能有唯一的辨識信息，而不需要通過中央控制端來做辨識信息。本文主要介紹 UUID 的生成算法，并且解釋它為什么能保證全局唯一。
為便于表示，UUID 標(biāo)準(zhǔn)型式包含 32 個 16 進(jìn)制數(shù)字，以連字號分為五段，形式為 8-4-4-4-12 的 32 個字符，例如：f81d4fae-7dec-11d0-a765-00a0c91e6bf6

1.node-uuid

下面的代碼是從node-uuid的v4算法簡化而得：

var _rnds = new Array(16);
var _byteToHex = [];
for (var i = 0; i < 256; i++) {
  _byteToHex[i] = (i + 0x100).toString(16).substr(1);
}

var _rng = function() {
  for (var i = 0, r; i < 16; i++) {
    if ((i & 0x03) === 0) { r = Math.random() * 0x100000000; }
    _rnds[i] = r >>> ((i & 0x03) << 3) & 0xff;
  }

  return _rnds;
};

function unparse(buf) {
  var i = 0, bth = _byteToHex;
  return  bth[buf[i++]] + bth[buf[i++]] +
          bth[buf[i++]] + bth[buf[i++]] + '-' +
          bth[buf[i++]] + bth[buf[i++]] + '-' +
          bth[buf[i++]] + bth[buf[i++]] + '-' +
          bth[buf[i++]] + bth[buf[i++]] + '-' +
          bth[buf[i++]] + bth[buf[i++]] +
          bth[buf[i++]] + bth[buf[i++]] +
          bth[buf[i++]] + bth[buf[i++]];
}


function v4() {
  // Deprecated - 'format' argument, as supported in v1.2
  var i = 0;

  var rnds = _rng();

  // Per 4.4, set bits for version and `clock_seq_hi_and_reserved`
  rnds[6] = (rnds[6] & 0x0f) | 0x40;
  rnds[8] = (rnds[8] & 0x3f) | 0x80;

  return unparse(rnds);
}
// 執(zhí)行
console.log(v4()); // e28427a9-f6ea-43f3-894d-ac9e48aaad49 // 去掉四個“-”后，還剩下32位

2.ckeditor5 uid.js

// A hash table of hex numbers to avoid using toString() in uid() which is costly.
// [ '00', '01', '02', ..., 'fe', 'ff' ]
const HEX_NUMBERS = new Array( 256 ).fill()
    .map( ( val, index ) => ( '0' + ( index ).toString( 16 ) ).slice( -2 ) );

/**
 * Returns a unique id. The id starts with an "e" character and a randomly generated string of
 * 32 alphanumeric characters.
 *
 * **Note**: The characters the unique id is built from correspond to the hex number notation
 * (from "0" to "9", from "a" to "f"). In other words, each id corresponds to an "e" followed
 * by 16 8-bit numbers next to each other.
 *
 * @returns {String} An unique id string.
 */
function uid() {
    // Let's create some positive random 32bit integers first.
    //
    // 1. Math.random() is a float between 0 and 1.
    // 2. 0x100000000 is 2^32 = 4294967296.
    // 3. >>> 0 enforces integer (in JS all numbers are floating point).
    //
    // For instance:
    //      Math.random() * 0x100000000 = 3366450031.853859
    // but
    //      Math.random() * 0x100000000 >>> 0 = 3366450031.
        // >>> 0可以保證是正數(shù)
    const r1 = Math.random() * 0x100000000 >>> 0;
    const r2 = Math.random() * 0x100000000 >>> 0;
    const r3 = Math.random() * 0x100000000 >>> 0;
    const r4 = Math.random() * 0x100000000 >>> 0;

    // Make sure that id does not start with number.
        // 跟0xFF的與操作可以確保只取8位，這樣確保從HEX_NUMBERS取到值
    return 'e' +
        HEX_NUMBERS[ r1 >> 0 & 0xFF ] +
        HEX_NUMBERS[ r1 >> 8 & 0xFF ] +
        HEX_NUMBERS[ r1 >> 16 & 0xFF ] +
        HEX_NUMBERS[ r1 >> 24 & 0xFF ] +
        HEX_NUMBERS[ r2 >> 0 & 0xFF ] +
        HEX_NUMBERS[ r2 >> 8 & 0xFF ] +
        HEX_NUMBERS[ r2 >> 16 & 0xFF ] +
        HEX_NUMBERS[ r2 >> 24 & 0xFF ] +
        HEX_NUMBERS[ r3 >> 0 & 0xFF ] +
        HEX_NUMBERS[ r3 >> 8 & 0xFF ] +
        HEX_NUMBERS[ r3 >> 16 & 0xFF ] +
        HEX_NUMBERS[ r3 >> 24 & 0xFF ] +
        HEX_NUMBERS[ r4 >> 0 & 0xFF ] +
        HEX_NUMBERS[ r4 >> 8 & 0xFF ] +
        HEX_NUMBERS[ r4 >> 16 & 0xFF ] +
        HEX_NUMBERS[ r4 >> 24 & 0xFF ];
}
console.log(uid()); // e80d81d97cc24b8b8bf6e2e7083167489，去掉開頭的e字母后，還剩32位

其他

function uuid() {
    var s = [];
    var hexDigits = "0123456789abcdef";
    for (var i = 0; i < 36; i++) {
        s[i] = hexDigits.substr(Math.floor(Math.random() * 0x10), 1);
    }
    // bits 12-15 of the time_hi_and_version field to 0010 
    s[14] = "4";
    // bits 6-7 of the clock_seq_hi_and_reserved to 01
    s[19] = hexDigits.substr((s[19] & 0x3) | 0x8, 1);
    s[8] = s[13] = s[18] = s[23] = "-";
 
    var uuid = s.join("");
    return uuid;
}
console.log(uuid()) // ea95751c-ccd0-418e-aac3-6bc408b76689

參考

理解 UUID