在document.body.scrollTop上链接到KnockoutObservable的触发器BindingHandler

I am attempting to trigger a Knockout BindingHandler as a direct result of the document.body.scrolltop value being greater or equal to a particular value. I have attempted to create an observable based on a statement. Firstly, is this possible? Or should I be updating the boolean result as part of a computed?I am attempting to trigger a Knockout BindingHa