Filter by hand

function filter(arr, filterCallback) {
  if (!Array.isArray(arr) || !arr.length || typeof filterCallback !== 'function') 
  {
    return [];
  } else {
    let result = [];
    for (let i = 0, len = arr.length; i < len; i++) {
      if (filterCallback(arr[i], i, arr)) {
        result.push(arr[i]);
      }
    }
    return result;
  }
}