Sometimes, we to find the nth occurrence of a character in a string in JavaScript.

In this article, we’ll look at how to find the nth occurrence of a character in a string in JavaScript.

How to find the nth occurrence of a character in a string in JavaScript?

To find the nth occurrence of a character in a string in JavaScript, we can use the string indexOf method with the from index argument.

For instance, we write:

const indexOfNth = (string, char, nth, fromIndex = 0) => {
  const indexChar = string.indexOf(char, fromIndex);
  if (indexChar === -1) {
    return -1;
  } else if (nth === 1) {
    return indexChar;
  } else {
    return indexOfNth(string, char, nth - 1, indexChar + 1);
  }
}

const str = 'foobarfoobaz'
console.log(indexOfNth(str, 'o', 3))

We define the indexOfNth function that recursively calls string.indexOf with fromIndex as the 2nd argument to start searching from fromIndex.

If indexOf returns -1, we return -1 since char isn’t in string.

If indexOf returns 1, then we found the index of the nth occurrence so we return indexChar.

Otherwise, we keep searching by calling indexOfNth with nth - 1 and indexChar + 1.

Therefore, 7 is logged from the console log since the 3rd o is at index 7.

Conclusion

To find the nth occurrence of a character in a string in JavaScript, we can use the string indexOf method with the from index argument.