记一次JS面试题

<script>
  var methodize = function (func, attr) {
    return function () {
      return func.apply(this, [(attr ? this[attr] : this)].concat([].slice.call(arguments)));
    };
  };

  var demethodize = function (fn) {
    return function () {
      var args = [].slice.call(arguments, 1); 
      return fn.apply(arguments[0], args)
    }
  };

  function add(i, j) { return i + j; }
  Number.prototype.add = methodize(add);
  console.log((3).add(4))
  console.log(demethodize(Number.prototype.add)(5, 6))
</script>