<!DOCTYPE html>
<html>
<body>
<p id="demo">Click the button to find out if the first attribute in this P element is an ID attribute</p>
<button onclick="myFunction()">Try it</button>
<script>
function myFunction() {
var x = document.getElementById("demo");
x.innerHTML = x.attributes[0].isId;
}
</script>
<p><strong>Note:</strong> The isId property is not supported in any of the major browsers.</p>
</body>
</html>