generate-next-name.js

var module = (function (exports) {
  var NameSequence,
      ZeroSequenceCache;

  NameSequence = '0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ'.split('');
  ZeroSequenceCache = [];

  function stringRepeat(str, num) {
      var result = '';

      for (num |= 0; num > 0; num >>>= 1, str += str) {
          if (num & 1) {
              result += str;
          }
      }

      return result;
  }

  function zeroSequence(num) {
      var res = ZeroSequenceCache[num];
      if (res !== undefined) {
          return res;
      }
      res = stringRepeat('0', num);
      ZeroSequenceCache[num] = res;
      return res;
  }

  function generateNextName(name) {
      var ch, index, cur;

      cur = name.length - 1;
      do {
          ch = name.charAt(cur);
          index = NameSequence.indexOf(ch);
          if (index !== (NameSequence.length - 1)) {
              return name.substring(0, cur) + NameSequence[index + 1] + zeroSequence(name.length - (cur + 1));
          }
          --cur;
      } while (cur >= 0);
      return 'a' + zeroSequence(name.length);
  }

  exports.generateNextName = generateNextName;

  return exports;
})({});

var name = 'a';
for (var i = 0; i < 10000000000; ++i) {
  print(name);
  name = module.generateNextName(name);
}