Regular Expression to reformat a US phone number in Javascript

Question

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:

Answer 1

thinking backwards

Take the last digits only (up to 10) ignoring first "1".

function formatUSNumber(entry = '') {
  const match = entry
    .replace(/\D+/g, '').replace(/^1/, '')
    .match(/([^\d]*\d[^\d]*){1,10}$/)[0]
  const part1 = match.length > 2 ? `(${match.substring(0,3)})` : match
  const part2 = match.length > 3 ? ` ${match.substring(3, 6)}` : ''
  const part3 = match.length > 6 ? `-${match.substring(6, 10)}` : ''    
  return `${part1}${part2}${part3}`
}

example input / output as you type

formatUSNumber('+1333')
// (333)

formatUSNumber('333')
// (333)

formatUSNumber('333444')
// (333) 444

formatUSNumber('3334445555')
// (333) 444-5555