Accessing the callback functions arguments

Question

 function wrapper(fn) { return function(...args) { console.log(args); fn.apply(this, args); return this; } } function Person() {} Person.prototype.setName = wrapper(function (first, last) { this.first = first; this.last = last; }) Person.prototype.sayName = function () { console.log(this.first + ' ' + this.last); } const p = new Person(); p.setName('John','Doe'); p.sayName(); 

in the sample code pattern, the console statement prints the arguments passed to the "wrapper" function (which is ["john", "doe"]). My confusion is how it can read the callback functions arguments in the returned function. Appreciate any pointer to help in understanding this.

Answer 1

This seems unnecessarily confusing piece of code, you could achieve the same result with much less code. That being said, it is because with apply you call a function (your callback function) with a given this value (which you already have) and arguments, which is an array in this case with the values of "John" and "Doe". You can read more about apply here .