im trying to do the reverse vowel challlange from leetcode, code looks good but its not working

with input 'hello', output should be 'holle'

heres my code,

var reverseVowels = function (s) {
  // change s into array
  // if a, i, u, e, o
  // change that item to 'marked'
  // also put the index of that marked items into another array
  // put the marked items to another array
  // sort that marked items array, then reverse it
  // // im at here right now
  // then put that array inside its original place

  let newString = s.split('');
  let markedItems = [];
  let markedItemsIndex = [];
  let count = 0;

  for (let i = 0; i < newString.length; i++) {
    if (
      newString[i] === 'a' ||
      newString[i] === 'i' ||
      newString[i] === 'u' ||
      newString[i] === 'e' ||
      newString[i] === 'o'
    ) {
      markedItemsIndex.push(i);
      markedItems.push(newString[i]);
      newString[i] = 'marked';
    }
  }

  let reversedMarkedItems = markedItems.reverse();

  for (let i = 0; i < newString.length; i++) {
    if (i === markedItemsIndex[count]) {
      console.log('here');
      newString[i] = reversedMarkedItems[count];
    }
    count++;
  }

  // return [newString, markedItems.reverse(), markedItemsIndex];
  return newString;
};

look at the second loop, im checking if the i === markedItemsIndex but my code never goes there, because of that, the 'here' never returns.

i've checked the type of i and type of markedItemsIndex, they're both a number. how can i fix this

You should only increment the count once the vowel at that index has been handled, i.e inside the if statement (not on every iteration, which causes a lot of them to be skipped).

if (i === markedItemsIndex[count]) {
    newString[i] = reversedMarkedItems[count];
    count++;
}

You also need to handle uppercase vowels as well, which can be checked more easily with a regular expression. Change the if statement in the first loop to:

if (/[aeiou]/i.test(s[i])) {
    // update markedItems...
}

Finally, use Array#join with an empty string to get a string as the result.

return newString.join('');

Move the count++ inside the if:

<!-- begin snippet: js hide: false console: true babel: false -->

<!-- language: lang-js -->

var reverseVowels = function (s) {
  let newString = s.split('');
  let markedItems = [];
  let markedItemsIndex = [];
  let count = 0;

  for (let i = 0; i < newString.length; i++) {
    if (
      newString[i] === 'a' ||
      newString[i] === 'i' ||
      newString[i] === 'u' ||
      newString[i] === 'e' ||
      newString[i] === 'o'
    ) {
      markedItemsIndex.push(i);
      markedItems.push(newString[i]);
      newString[i] = 'marked';
    }
  }

  let reversedMarkedItems = markedItems.reverse();

  for (let i = 0; i < newString.length; i++) {
    if (i === markedItemsIndex[count]) {
      newString[i] = reversedMarkedItems[count];
      count++;
    }
  }

  return newString.join(''); // Join the array back into a string
};

console.log(reverseVowels('hello')); // Output: "holle"

<!-- end snippet -->

You could use Array::unshift() to collect the vowels already in a reversed order:

<!-- begin snippet: js hide: false console: true babel: false -->

<!-- language: lang-js -->

const reverseVowels = str => {
  const arr = [...str], set = new Set([...'aeiouAEIOU']), vowels =[], indices = [];
  arr.forEach((char,idx)=>set.has(char) && vowels.unshift(char) && indices.push(idx));
  indices.forEach((idx, i) => arr[idx] = vowels[i]);
  return arr.join('');
};

console.log(reverseVowels('hello'));

<!-- end snippet -->