<!DOCTYPE html>
<html>
<body>
<p>Click the button to locate the first occurance of the letter "e".</p>
<button onclick="myFunction()">Try it</button>
<p id="demo"></p>
<script>
function myFunction() {
var str = "Hello world, welcome to the universe.";
var n = str.indexOf("e");
document.getElementById("demo").innerHTML = n;
}
</script>
</body>
</html>