Regular Expression to reformat a US phone number in Javascript

I'm looking to reformat (replace, not validate - there are many references for validating) a phone number for display in Javascript. Here's an example of some of the data:

• 123 4567890
• (123) 456-7890
• (123)456-7890
• 123 456 7890
• 123.456.7890
• (blank/null)
• 1234567890

Is there an easy way to use a regular expression to do this? I'm looking for the best way to do this. Is there a better way?

I want to reformat the number to the following: (123) 456-7890

Assuming you want the format "(123) 456-7890":

function formatPhoneNumber(phoneNumberString) {
  var cleaned = ('' + phoneNumberString).replace(/\D/g, '');
  var match = cleaned.match(/^(\d{3})(\d{3})(\d{4})$/);
  if (match) {
    return '(' + match[1] + ') ' + match[2] + '-' + match[3];
  }
  return null;
}

Here's a version that allows the optional +1 international code:

function formatPhoneNumber(phoneNumberString) {
  var cleaned = ('' + phoneNumberString).replace(/\D/g, '');
  var match = cleaned.match(/^(1|)?(\d{3})(\d{3})(\d{4})$/);
  if (match) {
    var intlCode = (match[1] ? '+1 ' : '');
    return [intlCode, '(', match[2], ') ', match[3], '-', match[4]].join('');
  }
  return null;
}
formatPhoneNumber('+12345678900') // => "+1 (234) 567-8900"
formatPhoneNumber('2345678900')   // => "(234) 567-8900"

Possible solution:

function normalize(phone) {
    //normalize string and remove all unnecessary characters
    phone = phone.replace(/[^\d]/g, "");

    //check if number length equals to 10
    if (phone.length == 10) {
        //reformat and return phone number
        return phone.replace(/(\d{3})(\d{3})(\d{4})/, "($1) $2-$3");
    }

    return null;
}

var phone = '(123)4567890';
phone = normalize(phone); //(123) 456-7890

var x = '301.474.4062';
    
x = x.replace(/\D+/g, '')
     .replace(/(\d{3})(\d{3})(\d{4})/, '($1) $2-$3');

alert(x);