filterMap.js

function filterMap(array, cb, predicate) {
    let idx = -1;
    const length = array.length;
    const result = [];
    for (; ++idx < length;) {
        const res = cb(array[idx], idx, array);
        const passes = predicate(res);
        if (!passes) {
          continue;
        };
        result[idx] = res;
        
    }
    return result;
};

filterMap.ts

type ItemCallback<T> = (item: T, index: number, array: Array<T>) => Partial<T>;

export function filterMap<T>(
  array: Array<T>,
  cb: ItemCallback<T>,
  predicate: (item: T) => boolean
): T[] {
  let idx = -1;
  const length = array.length;
  const result: T[] = [];
  for (; ++idx < length; ) {
    const res = cb(array[idx], idx, array);
    const passes = predicate(res);
    if (!passes) {
      continue;
    }
    result[idx] = res;
  }
  return result;
}