Add elements

<!DOCTYPE html>
<html>
<body>

<p>Click the button to see how many attributes the button element have.</p>

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

<p>The result should be 2 (the button element's id and onclick attributes).</p>

<p><strong>Note:</strong> In Internet Explorer 8 and earlier, the attributes property will return a collection of all <em>possible</em> attributes for the element, and will, in this example, display a much higher number than 2.</p>

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

<script>
function myFunction() {
  var x = document.getElementById("myBtn").attributes.length;
  document.getElementById("demo").innerHTML = x;
}
</script>

</body>
</html>