Tryit Editor v2.9

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

<p>This example uses the HTML DOM to assign an "onfocus" event to an input element.</p>

Enter your name: <input type="text" id="fname">

<script>
document.getElementById("fname").onfocus = function() {myFunction()};

function myFunction() {
    document.getElementById("fname").style.backgroundColor = "red";
}
</script>

</body>
</html>