Question

This is more of an exploratory question, seeing how the core JavaScript stuff works. I realize the convention is to not override any core JavaScript classes, but I just can’t seem to wrap my head around this one.

You can create what acts like “class methods” in JavaScript by adding to the core Function prototype like this:

Function.prototype.class_method = function() {
  console.log("class method called")
}

var User;
User = (function() {
  function User() {}
  return User;
})();

User.class_method(); // "class method called"

My question is, is there a way to add “instance methods” in a similar way? Something crazy like this, but what’s below doesn’t work (or make any sense):

alias = Function.prototype.constructor;
Function.prototype.constructor = function() {
  child = this;
  child.prototype.instance_method = function() {
    console.log("instance method called");
  }
  alias.apply(child);
}

var user = new User();
user.instance_method(); // method doesn't exist

It’s almost like you’d need to override the Function class’ constructor method and access the prototype from there. Is this possible?

It does work if you add to the Object.prototype like this:

Object.prototype.instance_method = function() {
  console.log("instance method");
}

var user = new User();
user.instance_method(); // "instance method called"

But that doesn’t seem right either, mainly because seeing the output in the node.js console from console.log({}); change is confusing:

console.log({});
// {};

Object.prototype.instance_method = function() {
  console.log("instance method");
}

console.log({});
// {"instance_method": [Function]}

Answer 1

If you are using node.js, you should be able to use Object.defineProperty ^[MDN] and make the new property non-enumerable:

Object.defineProperty(Object.prototype, 'instance_Method', {
    value: function() {
        console.log("instance method");
    },
    enumerable: false // it's already the default
});

This was introduced in ECMAScript5, so only newer browsers will support it.