<!DOCTYPE html>
<html>
<body id="test">

<button onclick="myFunction()">Try it</button>

<a href="/">/</a>
<a href="/home">/home</a>

<p id="demo"></p>

<script>
function myFunction() {
  var x = document.body.id;
  alert(x);
}
</script>

</body>
</html>