JS undefined and NULL checker not working

Question

     for(const id of this.extraRooms)
            {
              let doesRoomExist = document.getElementById('newRoomAddress' + newRoomId);
              //if(typeof(doesRoomExist) !== "null")              
               if(typeof(doesRoomExist) !== "undefined")
              {
                  const newRoomLabel = document.getElementById('newRoomAddress' + newRoomId).value        
             {

Probably a simple fix but if doesRoomExist is NULL it is still going inside the if statement...

let doesRoomExist = document.getElementById('newRoomAddress' + newRoomId);

will show doesRoomExist as NULL when stepping through the code in VS code, but show as undefined if used in developer tools...why is it going inside the if?

any help please?

Answer 1

You should check the value of doesRoomExist directly not its type, you can either check if (doesRoomExist !== null) or just doing if (doesRoomExist) will be enough;

if(doesRoomExist !== null)
    const newRoomLabel = document.getElementById('newRoomAddress' + newRoomId).value