Define AS for buttons on a different keyframe?

Question

This probably has an easy answer, but I seem to be unable to find it myself.
On frame 1 in the Timeline (in CS4), I have this actionscript:
var clickAreaLink1:URLRequest = new URLRequest("http://www.example.com/?=1");
btn_clickArea1.addEventListener(MouseEvent.CLICK, clickArea_click1);
function clickArea_click1(event:MouseEvent):void
        navigateToURL(clickAreaLink1,"_blank");
On a different keyframe, I have my button labled “btn_clickArea1.” When I run the movie I get the error “Cannot access a property or method of a null object reference.”
My guess is because the button is on a different keyframe than the actionscript. However, I have four buttons that will need to be constantly updated, so I want the actionscript all in one place to easily update them. Is there a good way to get this to work?
Thanks for your help!

Answer 1

The objects you want to have involved with code have to be in the presence of that code when it is processed in order to work.  So if you want all your code in frame 1, then all your content that uses that code must be in frame 1.  There is nothing wrong with spreading your code out as needed though.  As long as you dedicate a layer or two for actionscript, it should be easy to locate.
You set the "visible' property of movieclips, buttons, etc to true or false to control their visibility