decorator.js

// Implement a decorator function that takes 
// a function as an argument and will track
// how many times the passed function was called.

function Add(x, y) {
  return x + y; 
}

var addCallCount = countDecorator(Add);

Add(1, 1);
// -> 2 Dont pay attention to this number. The important part is we called the `Add` function once.
addCallCount();
// -> 1

Add(2, 2);
// -> 4 Dont pay attention to this number either. The important part is we called the `Add` function again.
addCallCount();
// -> 2