Index of substrings

Angelos Chalaris · JavaScript, String, Algorithm, Generator · Dec 31, 2020

Finds all the indexes of a substring in a given string.

  • Use Array.prototype.indexOf() to look for searchValue in str.
  • Use yield to return the index if the value is found and update the index, i.
  • Use a while loop that will terminate the generator as soon as the value returned from Array.prototype.indexOf() is -1.
const indexOfSubstrings = function* (str, searchValue) {
  let i = 0;
  while (true) {
    const r = str.indexOf(searchValue, i);
    if (r !== -1) {
      yield r;
      i = r + 1;
    } else return;
[...indexOfSubstrings('tiktok tok tok tik tok tik', 'tik')]; // [0, 15, 23]
[...indexOfSubstrings('tutut tut tut', 'tut')]; // [0, 2, 6, 10]
[...indexOfSubstrings('hello', 'hi')]; // []

Recommended snippets & collections

  • JavaScript generator functions are a more advanced yet very powerful JavaScript ES6 feature, which you can start using in your code right now.

  • Count substrings of string

    JavaScript, String

    Counts the occurrences of a substring in a given string.

  • Map string

    JavaScript, String

    Creates a new string with the results of calling a provided function on every character in the given string.

  • Palindrome

    JavaScript, String

    Checks if the given string is a palindrome.