Live Demo: JavaScript Handling the Focus Event

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<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="utf-8">
    <title>JavaScript Handling the Focus Event</title>
</head>
<body>
    <script>
        function highlightInput(elm){
            elm.style.background = "yellow";
        }    
    </script>
    <input type="text" onfocus="highlightInput(this)">
    <button type="button">Button</button>
</body>
</html>