Please help me understand find and replace function in javascript

I am new to javascript and learning it from fcc and another site called grasshopper.
I am met with a lesson about recursive replace function which I can’t understand.
So it goes like this.

var wrongDocument = "This document  ahs a typo in it. The other one ahs typo too.";
function changeSpelling(string, oldPart, newPart) {
  if (string.includes(oldPart) === false) {
    return string;
  string = string.replace(oldPart, newPart);
  return changeSpelling(string, oldPart, newPart);
console.log(changeSpelling(wrongDocument, 'ahs', 'has'));

I don’t understand why and how the return statement is calling the function that it is nestled in. What is happening here actually?
I also don’t understand the way we are writing the parameters and arguments.
Plus why this can’t be done with a if-else statement?

So I wrote my own code but I don’t know how correct it is.

var chat = "This document ahs a typo in it. The other one ahs too.";
var fix = (a, b) => {
    if (chat.includes(a) === false) {
        return chat;
    else {
        return chat.replace(a, b)

console.log(fix('ahs', 'has'));

Please explain the whole thing to me. Thank you.

Your solution will fix only 2 spelling errors. Instead the first one will parse all the words in the sentence. It calls itself with the rest of the sentence.

It cant be done only with if becouse we need a way to loop over the words. Recursion in that case

this is recursion, try looking it up. It is a pretty complex subject.