maskString.js

const maskedFirst4Char = (value: string): string => {
  return value.replace(/.(?=.{4})/g, '*');
}

const maskPhoneNumber = (phone: string): string => {
  if (!phone) return 'N/A';
  const code = phone.slice(0, 2);
  const number = phone.slice(2);
  const maskedFirst4Number = maskedFirst4Char(number)
    .replace(/.(?=(.{4})+$)/g, '$& '); // add a space after every 4 number
  return `+${code} ${maskedFirst4Number}`;
};