"arguments" keyword in JavaScript

const add = (x=5, y=10) => console.log(x+y);

After we run the transpiler on this code, here is what the output would look like:

"use strict";
var add = function add() {
 var x = arguments.length <= 0 || arguments[0] === undefined ?
 5 : arguments[0];
 var y = arguments.length <= 1 || arguments[1] === undefined ?
 10 : arguments[1];
 return console.log(x + y);
};

I got this snippet from Learning react book. I have two question here

1. Can arguments.length be negative?
2. Does checking the second "||" condition be sufficient to check whether arguments[0] or arguments[1] is undefined?