design patterns in Javascript - toggle functionality [duplicate]

My goal is to add some functionality to the bxslider script - in this case, I want to be able to enable/disable a keyboard event handler AFTER a slider is instantiated.

I guess this code is self explanatory, but it's ugly, it doesn't seem to be a good practice, and I have no idea of how to properly implement it. As you can see I'm very uncomfortable with that boolean argument which I don't know how to name it.

    el.toggleKeyboard = function(a_boolean_variable){
        if(!slider.initialized) return;
        slider.settings.keyboardEnabled = a_boolean_variable;
    }

I should call it slider.toggleKeyboard(true) to enable it and slider.toggleKeyboard(false) to disable it.

The private method related to it, which is called when the slider is instantiated:

  var setupKeyboard = function(){
         $(document).keydown(function(e){
             if (e.keyCode == 39) {
                 if (slider.settings.keyboardEnabled)
                    clickNextBind(e);
                 return false;
             }
             else if (e.keyCode == 37) {
                 if (slider.settings.keyboardEnabled)
                    clickPrevBind(e);
                 return false;
             }
         });
    }

Could anyone be so kind and shed a light on this for me? What design pattern should I use?

Thanks a lot!

EDIT

I came up with the following solution:

el.toggleKeyboard = function(shouldEnable){
    if(!slider.initialized) return;
    slider.settings.keyboardEnabled = (shouldEnable == undefined) ? !slider.settings.keyboardEnabled : shouldEnable;
}

It toggles keyboard navigation on/off and you can force by sending a boolean parameter (true to enable, false to disable).