function Coll(items) {
    this.removeItem = items.pop
}
const coll = new Coll([2,4,6,8,10])
console.log(coll.removeItem())

If I make console.log(coll), I can see that there's a function inside of the object. If I call it, it retuns undefined. I know the solution to make it run properly is to add () => items.pop() but I still can't understand why. The main question here is what happens when I add the () => ...() to the method call