Palindrome checker code, unexpected results

Iam trying to see if it is palindrome or not. ut is giving some unexpected responses

 let a=1221;
  a=a.toString();
  let c =[...a];
  let b=[...c].reverse();
  document.getElementById("demo").innerHTML = c==b;

What do you think […a] is doing when a is a string?

Hint: you need the .split and .join methods, and you do not need the spread operator anywhere.