Tryit Editor v2.9

Edit This Code:
<!DOCTYPE html>
<html>
<body>

<p>Click the button to locate the last occurance of a specified value.</p>

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

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

<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>