regex - Validate phone number using javascript

Question

I'm trying to validate phone number such as 123-345-3456 and (078)789-8908 using JavaScript. Here is my code

function ValidateUSPhoneNumber(phoneNumber) {
  var regExp = /^(([0-9]{3}) |[0-9]{3}-)[0-9]{3}-[0-9]{4}/;
  var phone = phoneNumber.match(regExp);
  if (phone) {
    alert('yes');
    return true;
  }
  alert('no');
  return false;
}

I'm testing the function using ValidateUSPhoneNumber('123-345-34567') which has 5 digits before the last hyphen which is invalid as per regex. But the function returns true. Can any one explain why?

Answer 1

JavaScript to validate the phone number:

function phonenumber(inputtxt) {
  var phoneno = /^(?([0-9]{3}))?[-. ]?([0-9]{3})[-. ]?([0-9]{4})$/;
  if(inputtxt.value.match(phoneno)) {
    return true;
  }
  else {
    alert("message");
    return false;
  }
}