上下滚动时显示和隐藏按钮

Question

please solve it if you can do, I made a function when I scroll down, I can show the "button" {this is basically an arrow which indicates from bottom to top}. I want to add another function that when I scroll down >500 it will show the button, and if I scroll up it will hide, and if I stop scrolling if my window is scrolled >500 it will show otherwise it will hide.

export default function ScrollToTop() {
const [isVisible, setIsVisible] = useState(false);
const ScrollToTop= () => {
    window.scrollTo({
    top: 0,
    behavior: "smooth"
    });
};
useEffect(() => {
    // Button is displayed after scrolling for 500 pixels
    const toggleVisibility = () => {
      if (window.pageYOffset > 500) {
        setIsVisible(true);
      } else {
        setIsVisible(false);
      }
    };
    window.addEventListener("scroll", toggleVisibility);

    return () => window.removeEventListener("scroll", toggleVisibility);
}, []);

  return (
  <div className="scroll-to-top">
    {isVisible && (
      <div  className="top" onClick={scrollToTop}>
        <div className="top_img_holder">
          <Image src="/uparrow.png" width="16" height="12"  alt="" />
        </div>
      </div>
    )}
  </div>
)
}

Answer 1

To add the behavior you described, you can try the following:

1. Add a useRef hook to store a reference to the previous scroll position.
2. Add an event listener for the scroll event in the component's useEffect hook, and update the component's state (using the setIsVisible function) based on the current and previous scroll positions.
3. Return the component's state (isVisible) from the useEffect hook's callback function, so that the effect is re-run whenever isVisible changes.

import { useState, useEffect, useRef } from "react";

export default function ScrollToTop() {
  const [isVisible, setIsVisible] = useState(false);
  const prevScrollPos = useRef(0);

  const scrollToTop = () => {
    window.scrollTo({
      top: 0,
      behavior: "smooth"
    });
  };

  useEffect(() => {
    const toggleVisibility = () => {
      const currentScrollPos = window.pageYOffset;

      // Button is displayed after scrolling for 500 pixels
      if (currentScrollPos > 500 && currentScrollPos > prevScrollPos.current) {
        setIsVisible(true);
      } else {
        setIsVisible(false);
      }

      prevScrollPos.current = currentScrollPos;
    };

    window.addEventListener("scroll", toggleVisibility);

    return () => window.removeEventListener("scroll", toggleVisibility);
  }, [isVisible]);

  return (
    <div className="scroll-to-top">
      {isVisible && (
        <div className="top" onClick={scrollToTop}>
          <div className="top_img_holder">
            <Image src="/uparrow.png" width="16" height="12" alt="" />
          </div>
        </div>
      )}
    </div>
  );
}