Edit in JSFiddle

document.onkeydown = checkShortcuts;

function checkShortcuts(event) {
    switch(event.keyCode){
        case 13:
            enterKeyPressed();
            break;
        case 27:
            escKeyPressed();
            break;
        default:
            break;
    }
}

function enterKeyPressed(){
        document.getElementById("action").innerHTML = "Enter Key Pressed";
}

function escKeyPressed(){
        document.getElementById("action").innerHTML = "Escape Key Pressed";
}

<html>
    
    <head></head>
    
    <body>
        <div>Key Code: <span id="action">Press Enter or Escape...</span>

        </div>
    </body>

</html>