Regular Expression to reformat a US phone number in Javascript

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"

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