Use the onfocus attribute to execute a script when the element gets focus in HTML.
Example
You can try to run the following code to implement the onfocus attribute −
<!DOCTYPE html>
<html>
<body>
<p>Enter subject name below,</p>
Subject: <input type = "text" id = "sname" onfocus = "display(this.id)">
<br>
<script>
function display(val) {
document.getElementById(val).style.background = "blue";
}
</script>
</body>
</html>