F8: Loops

I have many functions like this:

 
button.onRelease = function() {
if (_global.movieposition == "start") {
movie1_mc.gotoAndPlay ("end")
}

It seems to be that the function is playing only once. How do I get a function like this to check it over and over again? I know its something to do with while loops or for loops? Can someone tell me how I would write this code to apply it into my function described above?

Thank u