动画返回顶部

Tutorial: DOM实战 Category: JS Published: 2026-04-07 13:58:26 Views: 20 Likes: 0 Comments: 0
动画返回顶部.md

<!DOCTYPE html>
<html lang="en">
  <head>
    <style>
      .slider-bar {
        position: absolute;
        left: 50%;
        top: 300px;
        margin-left: 600px;
        width: 45px;
        height: 130px;
        background-color: pink;
      }

      .w {
        width: 1200px;
        margin: 10px auto;
      }

      .header {
        height: 150px;
        background-color: purple;
      }

      .banner {
        height: 250px;
        background-color: skyblue;
      }

      .main {
        height: 1000px;
        background-color: yellowgreen;
      }

      span {
        display: none;
        position: absolute;
        bottom: 0;
      }
    </style>
  </head>

  <body>
    <div class="slider-bar">
      <span class="goBack">返回顶部</span>
    </div>
    <div class="header w">头部区域</div>
    <div class="banner w">banner区域</div>
    <div class="main w">主体部分</div>
    <script>
      //1. 获取元素
      var sliderbar = document.querySelector(".slider-bar");
      var banner = document.querySelector(".banner");

      var bannerTop = banner.offsetTop;
      var sliderbarTop = sliderbar.offsetTop - bannerTop;

      var main = document.querySelector(".main");
      var goBack = document.querySelector(".goBack");
      var mainTop = main.offsetTop;

      // 2. 页面滚动事件 scroll
      document.addEventListener("scroll", function () {
        if (window.pageYOffset >= bannerTop) {
          sliderbar.style.position = "fixed";
          sliderbar.style.top = sliderbarTop + "px";
        } else {
          sliderbar.style.position = "absolute";
          sliderbar.style.top = "300px";
        }

        // 4. 当我们页面滚动到main盒子, 就显示 goback模块
        if (window.pageYOffset >= mainTop) {
          goBack.style.display = "block";
        } else {
          goBack.style.display = "none";
        }
      });

      // 3. 当我们点击了返回顶部模块, 就让窗口滚动的页面的最上方
      goBack.addEventListener("click", function () {
        // 里面的x和y 不跟单位的 直接写数字即可
        // window.scroll(0, 0);
        // 因为是窗口滚动 所以对象是window
        animate(window, 0);
      });

      // 动画函数
      function animate(obj, target, callback) {
        clearInterval(obj.timer);

        obj.timer = setInterval(function () {
          var step = (target - window.pageYOffset) / 10;
          step = step > 0 ? Math.ceil(step) : Math.floor(step);

          if (window.pageYOffset == target) {
            clearInterval(obj.timer);
            callback && callback();
          }

          window.scroll(0, window.pageYOffset + step);
        }, 15);
      }
    </script>
  </body>
</html>
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