Why this arrow function doesn't work with 'arguments.length'?

Question

I'm wondering why the following arrow function, named 'countArg2' doesn't work. Is there anybody can explain what's wrong please?

---

This works

function countArg1() {
    return arguments.length;
}
countArg1(1, 2, 3);   //3

This doesn't work..

const countArg2 = () => arguments.length;
countArg2(1, 2, 3);
// Uncaught ReferenceError: arguments is not defined

Thank you in advance.

Answer 1

You have to parse the arguments to the arrow function like this

const countArg2 = (...arguments) => arguments.length;
console.log(countArg2(1, 2, 3));
 // VM6745:1 Uncaught ReferenceError: arguments is not defined
 // at mArgs (<anonymous>:1:29)
 // at <anonymous>:2:1