lastIndexOf() : Find last occurance of the value inside string in JavaScript

JS Script :

<html>
<body>
<script type="text/javascript">
var str="Pritesh Taral";
document.write(str.lastIndexOf("r") + "<br />");
document.write(str.lastIndexOf("TARAL") + "<br />");
document.write(str.lastIndexOf("Taral"));
</script>
</body>
</html>

output in Browser :

10
-1
8