Filter an array and split the array into 2 arrays, one with the elements matching the predicate and one with the elements rejected by the predicate

filterSplit.ts

// const filteredArray = myArray.filter(str => str.length > 255);
// becomes
// const [filteredArray, rejectedArray] = myArray.filterSplit(str => str.length > 255);

declare global {
  interface Array<T> {
    filterSplit(predicate: (item: T, index: number, array: T[]) => boolean): [T[], T[]];
  }
}

Array.prototype.filterSplit = function<T>(predicate: (item: T, index: number, array: T[]) => boolean): [T[], T[]] {
  const matched: T[] = [];
  const rejected: T[] = [];

  this.forEach((item, index, array) => {
    if (predicate(item, index, array)) {
      matched.push(item);
    } else {
      rejected.push(item);
    }
  });

  return [matched, rejected];
};