How to use Javascript .replace() method within a for loop?

I am attempting to take a given string and replace a given number in that string with a character. Specifically:

• 5 is to be replaced with "S"
• 1 is to be replaced with "I"
• 0 is to be replaced with "O"

(this is a Kata exercise)

I have written a function which should:

1. Take the string and convert it into an array
2. Loop over the array
3. Replace each instance of the aforementioned numbers with the appropriate replacements using .replace()
4. Return the joined string.

My code is as appears below

Function correct(string) {
let array = string.split('')
  for (let i = 0; i < array.length; i++) {
    array[i].replace('5', 'S')
    array[i].replace('0', 'O')
    array[i].replace('1', 'I')
  }
  return array.join('');
}

The function returns the string exactly as initially provided, unchanged. I suspect my issue is with the way I’ve used the .replace() method within the loop, or the index positions declared.

>Solution :

String.prototype.replace returns a new string and does not mutate the variable it was executed on.
That’s why you need to assign the result of replacement somewhere.

To fix your code just do the following with each replacement:

array[i] = array[i].replace('5', 'S');

Note 1: since array[i] is always a single character, there is no need in replace, because you can just compare like so:

if (array[i] === '5') {
  array[i] = 'S';
}

or oneliner:

array[i] = array[i] === '5' ? 'S' : array[i];

Note 2: for loop for a replacement is not a clean code. JavaScript is very flexible and provides much better solutions to the problem. Eg. String.prototype.replaceAll.