<!DOCTYPE html>
<html>
<body>
<p>This example demonstrates how to assign an "onkeydown" event to an input element.</p>
<p>Press a key inside the text field to set a red background color.</p>
<input type="text" id="demo" onkeydown="myFunction()">
<script>
function myFunction() {
document.getElementById("demo").style.backgroundColor = "red";
}
</script>
</body>
</html>