Generate Firebase IDs using the same approach as Firebase.push()

firebaseID.js

var ALPHABET = '-0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ_abcdefghijklmnopqrstuvwxyz';

function generateFirebaseID() {
  var timestamp = +new Date();
  var chars = Array(20);
  for (var i = 7; 0 <= i; i--) {
    chars[i] = ALPHABET.charAt(timestamp % 64);
    timestamp = Math.floor(timestamp / 64);
  }

  for (var j = 0; 12 > j; j++) {
    chars[8 + j] = ALPHABET.charAt(Math.floor(64 * Math.random()));
  }

  return chars.join('');
}