About jquery in event.keyCode and event.ctrlKey shortcuts and prevent conflict

In the keydown event, event.which return ASCII code

　　　　　　　　　event.ctrlKey return boolean

$(document).keydown(function(event){

　　var ctrl = event.ctrlKey; // If you click the Ctrl key, ctrl is true

　　switch（event.keyCode）{};   　　　　

　　return false; // returns false to prevent conflict shortcuts

}) // keydown can only pass a key