Returns the head of a list.
Use arr[0] to return the first element of the passed array.
const head = arr => arr[0];
head([1, 2, 3]); // 1 -
Returns all indices of val in an array. If val never occurs, returns [-1].
Use Array.forEach() to loop over elements and Array.push() to store indices for matching elements. Return [-1] if length of the array of indices is 0, otherwise return the array of indices.
const indexOfAll = (arr, val) => { +
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;