Tryit Editor v2.9

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

<p>Click the button to extract the first character from the string.</p>

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

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

<script>
function myFunction() {
    var str = "Hello world!"; 
    var res = str.substring(0, 1);
    document.getElementById("demo").innerHTML = res;
}
</script>

</body>
</html>