Phone Number formatting with RegExps

instructions.js

// Let's say we have US phone numbers in forms:
// 1222333444 and 2223334444
//
// We need to format them in a form:
// 1-(222)-333-4444

// Step 1: prepend phone number with '1' if it's in a short form:

var phone = '2223334444';

phone = phone.replace(/(\d{10})/g, '1$1');

phone === '12223334444';

// Step 2: split the phone number into chunks

phone = phone.replace(/(\d)(\d{3})(\d{3})(\d{4})/g, '$1-($2)-$3-$4');

phone === '1-(222)-333-4444'