stopping a nested javascript function running more than once

I'm trying to get a javascript function to run only once. I've seen this question has been asked before, e.g. Function in javascript that can be called only once, but I can't get the solutions in here to work. I'm not sure if it's because I've got nested functions, or whether there's something I'm missing. Essentially, I'm trying to run a function which, when a webpage is scrolled, it: - runs a little animation on a canvas in the header - reduces the size of the header - leaves it at that

But when there is any subsequent scrolling, the animation keeps re-running. Here's a summarised version of the non-working code:

$(document).on("scroll",function(){

    var arrange_title = function(){

        //some code 
    };

    if($(document).scrollTop()>0){ 
        arrange_title();
        arrange_title = function(){};
        setTimeout(function(){
            $("header").removeClass("large").addClass("small");
        },1000);
    }
});

I've also tried declaring a global variable, setting it to "false" in a "window.onload" function, then set it to true in an if function that runs the animation (the if function running only if the variable is false), but that doesn't stop it either. Thoughts?