Reverse a string issue - join function does not seem to work

I was wondering if I could tag onto this artical and ask someone to explain to me why this doesn’t work. I can make it work in 5 or 6 different ways but I don’t understand why it doesn’t work this way.

function reverseString(str) {
var string = str.split("");
string.reverse();
string.join(’’);
return string;
}

reverseString(“hello”);