参考: http://docs.python.jp/3.3/library/functions.html#enumerate

enumerate.js

(function () {
  var count = function (start) {
    start = start || 0;

    return function () {
      return start++;
    };
  };

  var enumerate = function (iter, start) {
    var result = [];
    var cnt = count(), i;

    return function () {
      i = cnt();
      if (typeof iter[i] !== 'undefined') {
        return [i, iter[i]];
      }
    };
  };

  this.enumerate = enumerate;
}).call(this)