30-seconds-of-code/snippets/indexOfAll.md

indexOfAll

Returns all indices of val in an array. If val never occurs, returns [].

Use Array.forEach() to loop over elements and Array.push() to store indices for matching elements. Return the array of indices.

const indexOfAll = (arr, val) => {
  const indices = [];
  arr.forEach((el, i) => el === val && indices.push(i));
  return indices;
};

indexOfAll([1, 2, 3, 1, 2, 3], 1); // [0,3]
indexOfAll([1, 2, 3], 4); // []