findFirstN

Finds the first n elements for which the provided function returns a truthy value.

• Use a for..in loop to execute the provided matcher for each element of arr.
• Use Array.prototype.push() to append elements to the results array and return them if its length is equal to n.

const findFirstN = (arr, matcher, n = 1) => {
  let res = [];
  for (let i in arr) {
    const el = arr[i];
    const match = matcher(el, i, arr);
    if (match) res.push(el);
    if (res.length === n) return res;
  }
  return res;
};

findFirstN([1, 2, 4, 6], n => n % 2 === 0, 2); // [2, 4]
findFirstN([1, 2, 4, 6], n => n % 2 === 0, 5); // [2, 4, 6]