Edit in JSFiddle

document.onkeydown = checkShortcuts;

function checkShortcuts(event) {
    document.getElementById("action").innerHTML = event.keyCode;
}

<html>
    
    <head></head>
    
    <body>
        <div>Key Code: <span id="action">Press any key...</span>

        </div>
    </body>

</html>