function onScroll()

in modules/closure/sticky/sticky.js [224:282]
32 lines of code
17 McCabe index (conditional complexity)

    function onScroll() {
      var scrollTop = contentEl.prop('scrollTop');
      var isScrollingDown = scrollTop > (onScroll.prevScrollTop || 0);

      // Store the previous scroll so we know which direction we are scrolling
      onScroll.prevScrollTop = scrollTop;

      //
      // AT TOP (not scrolling)
      //
      if (scrollTop === 0) {
        // If we're at the top, just clear the current item and return
        setCurrentItem(null);
        return;
      }

      //
      // SCROLLING DOWN (going towards the next item)
      //
      if (isScrollingDown) {

        // If we've scrolled down past the next item's position, sticky it and return
        if (self.next && self.next.top <= scrollTop) {
          setCurrentItem(self.next);
          return;
        }

        // If the next item is close to the current one, push the current one up out of the way
        if (self.current && self.next && self.next.top - scrollTop <= self.next.height) {
          translate(self.current, scrollTop + (self.next.top - self.next.height - scrollTop));
          return;
        }
      }

      //
      // SCROLLING UP (not at the top & not scrolling down; must be scrolling up)
      //
      if (!isScrollingDown) {

        // If we've scrolled up past the previous item's position, sticky it and return
        if (self.current && self.prev && scrollTop < self.current.top) {
          setCurrentItem(self.prev);
          return;
        }

        // If the next item is close to the current one, pull the current one down into view
        if (self.next && self.current && (scrollTop >= (self.next.top - self.current.height))) {
          translate(self.current, scrollTop + (self.next.top - scrollTop - self.current.height));
          return;
        }
      }

      //
      // Otherwise, just move the current item to the proper place (scrolling up or down)
      //
      if (self.current) {
        translate(self.current, scrollTop);
      }
    }