전화번호 포맷팅 — replace 는 매치된 부분만 바꾸고 나머지는 뒤에 그대로 남긴다. 그래서 그룹 자릿수 합이 길이와 같아야 한다1

function formatPhoneNumber(phoneNumber) {
  const cleaned = phoneNumber.replace(/\D/g, '')

  if (cleaned.length === 11) {
    return cleaned.replace(/(\d{3})(\d{4})(\d{4})/, '$1-$2-$3')
  } else if (cleaned.length === 10 && cleaned.startsWith('02')) {
    return cleaned.replace(/(\d{2})(\d{4})(\d{4})/, '$1-$2-$3')
  } else if (cleaned.length === 10) {
    return cleaned.replace(/(\d{3})(\d{3})(\d{4})/, '$1-$2-$3')
  } else if (cleaned.length === 9 && cleaned.startsWith('02')) {
    return cleaned.replace(/(\d{2})(\d{3})(\d{4})/, '$1-$2-$3')
  }
  return 'Invalid phone number'
}

formatPhoneNumber('01012341234') // 010-1234-1234
formatPhoneNumber('021234567') // 02-123-4567
formatPhoneNumber('0212345678') // 02-1234-5678

Footnotes

  1. String.prototype.replace() - MDN: “returns a new string with one, some, or all matches of a pattern replaced by a replacement.” ↩

#javascript#regex#formatting
#323

거리 만km 포맷팅 — toFixed(1) 은 반올림하고 0 까지 채운 문자열을 준다(100000 → 10.0만km)1

function formatToManKm(distance: number): string {
  const manKm = (distance / 10000).toFixed(1)

  return `${manKm}만km`
}

formatToManKm(104335) // "10.4만km"

Footnotes

  1. Number.prototype.toFixed() - MDN: “The number is rounded if necessary, and the fractional part is padded with zeros if necessary so that it has the specified length.” ↩

#javascript#formatting
#325