<!DOCTYPE html>
<html lang="en-US">
<body>
<p>P 1</p>
<p>P 2</p>
<p>P 3</p>
<button onclick="myFunction()">Click Me</button>
<script>
function myFunction(){
var x = document.getElementsByTagName("p");
x[0].innerHTML = "Tag Length : "+x.length;
}
</script> </body>
</html>