What does a comma do in JavaScript expressions?

Question

If I use:

1.09 * 1; // returns \"1.09\"

But if I use:

1,09 * 1; // returns \"9\"

I know that 1,09 isn\'t

Answer 1

Some more to consider:

console.log((0, 9));
console.log((9, 0));
console.log(("foo", "bar"));