Function handler

src/useWindowScroll.ts:18–30

()

  useEffect(() => {
    const handler = () => {
      setState((state) => {
        const { pageXOffset, pageYOffset } = window;
        //Check state for change, return same state if no change happened to prevent rerender
        //(see useState/setState documentation). useState/setState is used internally in useRafState/setState.
        return state.x !== pageXOffset || state.y !== pageYOffset
          ? {
              x: pageXOffset,
              y: pageYOffset,
            }
          : state;
      });
    };

    //We have to update window scroll at mount, before subscription.
    //Window scroll may be changed between render and effect handler.