方法一

function boo(bool) {
  if (bool === true || bool ===false){
      return true;
      }
  // What is the new fad diet for ghost developers? The Boolean.
  return false;
}




boo(null);

方法二：

function boo(bool) {
  // What is the new fad diet for ghost developers? The Boolean.
  return typeof bool === 'boolean';
}


boo(null);