Delay-execute any existing function by a call of the form "function_name.callAfter(ms, param1, param2, ...)"

I recently got an interview question, that I failed to answer correctly. Here it goes:

Write an implementation of a function callAfter that enables ANY function to be called after some specified duration. The output of the function should remain the same. The function should have > following syntax:

Example 1: Let's say you have a function called sum like so:

function sum(a, b) {
 console.log('Sum is: ', a + b);
}

Now you should be able to execute:

sum.callAfter(5000, 8, 9);

This should invoke the function sum after 5 seconds with parameters 8 and 9. Output: 'Sum is: 17'.

Example 2: For a function difference with the following implementation:

function difference(a, b) {
  console.log('Difference is: ', a-b);
}

You should be able to execute:

difference.callAfter(4000, 8, 6);

This should invoke the function difference after 4 seconds with parameters 8 and 6. Output: 'Difference is: 2'.

NOTE: I am aware that I could execute a function after n seconds using something like:

var delay_func = (function(){
  var timer = 0;
  return function(callback, ms){
    clearTimeout (timer);
    timer = setTimeout(callback, ms);
  };
})();

However, I was asked to attach a callAfter 'sub-function' with every function to facilitate the call:

<function_name>.callAfter(milliseconds, param1, param2, ...);

You can do it by adding a method to the function constructor's prototype object. That way any created function can inherit that method. It's referred to as prototypal inheritance:

Function.prototype.callAfter = function(delay, ...args) {
    setTimeout(() => this(...args), delay)
};