In this example the index() is an inbuilt method in jQuery which is used to return the index of the a specified elements with respect to selector.
<!DOCTYPE html>
<html>
<head>
<script src="https://ajax.googleapis.com/ajax/libs/jquery/3.3.1/jquery.min.js">
</script>
<script>
$(document).ready(function() {
$("li").click(function() {
document.getElementById("demo").innerHTML = "Clicked Index " + $(this).index();
});
});
</script>
</head>
<body>
<h1>Click on the elements of the list to display their index
number with respect to the other elements in the list.</h1>
<h1 style="color:crimson"> APPWRK Service
<ul>
<li>Web Service</li>
<li>Web development</li>
<li>Mobile app development</li>
</ul>
</h1>
<h1 id="demo" style="color: rgb(32, 24, 145)"></h1>
</body>
</html>
