The onkeydown event triggers when a key is pressed. You can try to run the following code to learn how to work with an onkeydown event in JavaScript −
Example
<html>
<head>
<script>
<!--
function sayHello() {
alert("A key is pressed.")
}
//-->
</script>
</head>
<body>
<input type = "text" onkeydown = "sayHello()">
</body>
</html>