<html>
<body>
<p id="demo">Click the button to locate the last occurance of a specified value.</p>
<button onclick="myFunction()">Try it</button>
<script>
function myFunction()
{
var str="Hello planet earth, you are a great planet.";
var n=str.lastIndexOf("planet");
document.getElementById("demo").innerHTML=n;
}
</script>
</body>
</html>