When the user pushes the ? key, QuestionMark.js triggers a modal window that displays keyboard shortcuts for your app — similar to what happens on Twitter, Gmail, GitHub, etc. The modal is removed when the ESC key is pushed or the user clicks behind the modal.I think every app that has keyboard shortcuts should do this. This could also be a generic ‘help’ menu for the app, but that would require some tweaking to the code and the CSS. For now, this works primarily as a shortcut keys menu.
Core Java Script Popup Window