Use the onkeydown attribute. The onkeydown attribute triggers when the user is pressing a key.
Example
You can try to run the following code to execute a script on pressing a key −
<!DOCTYPE html>
<html>
<body>
<p>Press a key inside the textbox.</p>
<input type = "text" onkeydown = "display()">
<script>
function display() {
alert("You pressed a key!");
}
</script>
</body>
</html>