Increment localStorage value by one

I am working on an attempted log in feature to our application. They fail three times it kicks them out altogether. To keep count of how many times they attempt I thought I would use localStorage because I can easily manipulate it. However, I am having trouble incrementing the value when they fail to authenticate themselves.

At the top, I am setting the localStorage variable

localStorage.setItem("attempts", "0")

and then if the server returns an error, I am trying to increment that value.

if(errorCode === 4936){
  var attempts = localStorage.getItem("attempts");
  localStorage.setItem(attempts++);
  console.log(attempts);
}

and obviously this is not working, but all I can find when I research is setting and getting the localStorage nothing about updating or changing. Any help would be wonderful!

Answer

And in some cases you have to add ++ before attempts:

if (errorCode == 4936) {
  var attempts = parseInt(localStorage.getItem("attempts"));
  localStorage.setItem("attempts", ++attempts);
  console.log(attempts);
}