Question

How do you reverse a string in place in JavaScript when it is passed to a function with a return statement, without using built-in functions (.reverse(), .charAt() ?

Answer 1

As you are dealing with simple ASCII characters just try this:

function reverse(s){
    return s.split("").reverse().join("");
}

If you want something that supports UTF-16 then it's a bad choice that will give invalid Unicode strings or valid strings that look funny.

I hope this helps you.