only_modifier_event = function(event){
        /**
         * Return `true` if the event only contains modifiers keys.
         * false otherwise
         **/
        var key = inv_keycodes[event.which];
        return ((event.altKey || event.ctrlKey || event.metaKey || event.shiftKey) && 
         (key === 'alt'|| key === 'ctrl'|| key === 'meta'|| key === 'shift'));

    }
Convert a shortcut (shift-r) to a jQuery Event object