browser-cuid.js

/**
 * cuid.js
 * Collision-resistant UID generator for browsers and node.
 * Sequential for fast db lookups and recency sorting.
 * Safe for element IDs and server-side lookups.
 *
 * Extracted from CLCTR
 *
 * Copyright (c) Eric Elliott 2012
 * MIT License
 */

/*global window, navigator, document, require, process, module */
(function (app) {
  'use strict';
  var namespace = 'cuid',
    c = 0,
    blockSize = 4,
    base = 36,
    discreteValues = Math.pow(base, blockSize),

    pad = function pad(num, size) {
      var s = "000000000" + num;
      return s.substr(s.length-size);
    },

    randomBlock = function randomBlock() {
      return pad((Math.random() *
            discreteValues << 0)
            .toString(base), blockSize);
    },

    safeCounter = function () {
      c = (c < discreteValues) ? c : 0;
      c++; // this is not subliminal
      return c - 1;
    },

    api = function cuid() {
      // Starting with a lowercase letter makes
      // it HTML element ID friendly.
      var letter = 'c', // hard-coded allows for sequential access

        // timestamp
        // warning: this exposes the exact date and time
        // that the uid was created.
        timestamp = (new Date().getTime()).toString(base),

        // Prevent same-machine collisions.
        counter,

        // A few chars to generate distinct ids for different
        // clients (so different computers are far less
        // likely to generate the same id)
        fingerprint = api.fingerprint(),

        // Grab some more chars from Math.random()
        random = randomBlock() + randomBlock();

        counter = pad(safeCounter().toString(base), blockSize);

      return  (letter + timestamp + counter + fingerprint + random);
    };

  api.slug = function slug() {
    var date = new Date().getTime().toString(36),
      counter,
      print = api.fingerprint().slice(0,1) +
        api.fingerprint().slice(-1),
      random = randomBlock().slice(-2);

      counter = safeCounter().toString(36).slice(-4);

    return date.slice(-2) +
      counter + print + random;
  };

  api.globalCount = function globalCount() {
    // We want to cache the results of this
    var cache = (function calc() {
        var i,
          count = 0;

        for (i in window) {
          count++;
        }

        return count;
      }());

    api.globalCount = function () { return cache; };
    return cache;
  };

  api.fingerprint = function browserPrint() {
    return pad((navigator.mimeTypes.length +
      navigator.userAgent.length).toString(36) +
      api.globalCount().toString(36), 4);
  };

  // don't change anything from here down.
  if (app && app.register) {
    app.register(namespace, api);
  } else if (typeof module !== 'undefined') {
    module.exports = api;
  } else {
    app[namespace] = api;
  }

}(this));