Javascript - Online Coding assessment to mask credit cards numbers with # [duplicate]

Question

I got the below coding assessment question in Javascript. I tried my best to solve but there are few edge cases I missed. I need help to identify those missing cases

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.

This is what I tried so far

function maskify (cc) {
  if (cc.length < 6) {
      let reversed = reverse(cc);
      let newString = '';
      for (let i = 0; i < reversed.length; i++) {
        if (i < 4) {
          newString += reversed[i];
        } else {
          newString += '#';
        }
      }
      return reverse(newString);

Output

Answer 1

This is my solution:

function maskify (cc) {
  // If less than 6 characters return full number
  if (cc.length < 6)
    return cc;
    
  // Take out first character
  let firstChar = cc.charAt(0);
  cc = cc.slice(1);
    
  // Replace characters except last 4
  cc = cc.replace(/\d(?=.{4,}$)/g, '#');
  
  // Add first character back
  cc = firstChar + cc;
  
  return cc;
}

// Run every example number
const tests = ["4556364607935616", "4556-3646-0793-5616", 
                "64607935616", "ABCD-EFGH-IJKLM-NOPQ",
                "A1234567BCDEFG89HI", "12345", "", "Skippy"];

tests.forEach((number) => console.log(`Testing: ${number} - Output: ${maskify(number)}`));

I ran it with all the numbers of your example and it gets the correct output.