I am trying to learn JavaScript and currently stuck on a question about how would I rewrite brad's code using the split method and bug does brad have in his code? can you please help? Here is the code

function validate(phoneNumber) { 
  if (phoneNumber.length > 8 ||
      phoneNumber.length < 7) {
      return false;
  }
  var first = phoneNumber.substring(0,3);
  var second = phoneNumber.substring(phoneNumber.length - 4);
  
  if (isNaN(first) || isNaN(second)) {
  return false;
  }
  if (phoneNumber.length === 8) {
     return (phoneNumber.charAt(3) === "-");
  } 
  return true;

}

var number= validate("123-6778");
console.log(number);

Page the question and the code is on