takeRightUntil

Removes elements from the end of an array until the passed function returns true. Returns the removed elements.

• Create a reversed copy of the array, using the spread operator (...) and Array.prototype.reverse().
• Loop through the reversed copy, using a for...of loop over Array.prototype.entries() until the returned value from the function is truthy.
• Return the removed elements, using Array.prototype.slice().
• The callback function, fn, accepts a single argument which is the value of the element.

const takeRightUntil = (arr, fn) => {
  for (const [i, val] of [...arr].reverse().entries())
    if (fn(val)) return i === 0 ? [] : arr.slice(-i);
  return arr;
};

takeRightUntil([1, 2, 3, 4], n => n < 3); // [3, 4]