Q.

Description:
Usually when you buy something, you're asked whether your credit card number, phone number or answer to your most secret question is still correct. However, since someone could look over your shoulder, you don't want that shown on your screen. Instead, we mask it.

Your task is to write a function maskify, which changes all but the last four characters into '#'.

Examples
maskify("4556364607935616") == "############5616"
maskify( "64607935616") == "#######5616"
maskify( "1") == "1"
maskify( "") == ""

// "What was the name of your first pet?"
maskify("Skippy") == "##ippy"
maskify("Nananananananananananananananana Batman!") == "####################################man!"

A)

// return masked string
function maskify(cc) {
  if(cc.length > 4) {
    return '#'.repeat(cc.length-4) + cc.slice(-4)
  } 
  return cc
}

새로 배운 것

String.prototype.padStart()
padStart() 메서드는 현재 문자열의 시작을 다른 문자열로 채워, 주어진 길이를 만족하는 새로운 문자열을 반환합니다. 채워넣기는 대상 문자열의 시작(좌측)부터 적용됩니다.

완전신기신기