Javascript Spread in function calls

Question

Could someone explain why do we need "null" in this case? And how to use apply for a function? Thank you.
function myFunction(w,x,y,z) {
console.log(w+x+y+z);
}
var args = [1,2,3];
myFunction.apply(null, args.concat(4));

Answer 1

apply() method takes two arguments. First an object, in this case myFunction will be called as that objects method, and second argument is an array. Here you just want to call a function independently using apply. So you have to specify null, so that it does not throw an error.

Since you don't have a this keyword in myFunction you can use any object instead of null as a first argument

Answer 2

in es6 we can rather use the spread operator to apply an array as arguments of a function:

myFunction(...args.concat(4));

or even:

myFunction(...args,4);

.apply() method should be reserved for very specific cases...