en.javascript.info/1-js/02-first-steps/10-ifelse/4-check-login/solution.md

let userName = prompt("Who's there?", '');

if (userName == 'Admin') {

  let pass = prompt('Password?', '');

  if (pass == 'TheMaster') {
    alert( 'Welcome!' );
  } else if (pass == null || pass == '') { // (*)
    alert( 'Canceled.' );
  } else {
    alert( 'Wrong password' );
  }

} else if (userName == null || userName == '') { // (**)

  alert( 'Canceled' );

} else {

  alert( "I don't know you" );

}

Please note the if check in lines (*) and (**). Every browser except Safari returns null when the input is canceled, and Safari returns an empty string. So we must treat them same for compatibility.

Also note the vertical indents inside the if blocks. They are technically not required, but make the code more readable.