Can I overwrite a constructor in javascript?

Question

I just learned that I can overwrite a method in a Javascript class, as shown below, but what about the actual constructor?

If possible, how do I do it without instantiating the class?

var UserModel = (function() {
  var User;
  User = function() {}; // <- I want to overwrite this whilst keeping below methods
  User.prototype.isValid = function() {};
  return User;
})();

Answer 1

Just temporarily save the prototype object, and then replace the constructor function:

var proto = UserModel.prototype;
UserModel = function () { /* new implementation */ };
UserModel.prototype = proto;