Why my method is not reversing the string

February 12, 2023

I know there are many other ways to reverse a string in JS but I wrote this and it is not working and I want to understand why. Mine only has two extra parameters so I can tell it to reverse from here to there.

function strRev(str, startRev, endRev) {
    while (startRev < endRev) {
        let temp = str[startRev];
        str[startRev] = str[endRev]; 
        str[endRev] = temp;

        startRev += 1; 
        endRev -= 1;
    }
    return str;
}

And usage:

let str = "STACK";
strRev(str, 0, str.length -1 );

But what I get as result is the same original string. I don’t understand why.

It works when I trace it on paper.

>Solution :

You can not set the character of a string using the index with bracket notation.

To do what you are trying to do, you need to use an array and not a string.

function strRev(orgStr, startRev, endRev) {
  const str = orgStr.split('');
  while (startRev < endRev) {
    let temp = str[startRev];
    str[startRev] = str[endRev];
    str[endRev] = temp;

    startRev += 1;
    endRev -= 1;
  }
  return str.join('');
}


let str = "STACK";
console.log(strRev(str, 0, str.length - 1));