javascript - 在滚动上固定/修复 Vanilla Javascript 中的多个元素

Question

我是 javascript 的初学者，我正在尝试使用 es6 规范构建一些东西。

我想在向下滚动页面时重新创建 ScrollMagic 的固定效果并固定不同的部分。

所以我有这个简单的 html 标记，其中包含页眉、页脚和 3 个部分:

<header class="forewords">
 <h1>Some text</h1>
</header>

<div class="wrapper">
 <section class="project" id="item1">this is section 1</section>
 <section class="project" id="item2">this is section 2</section>
 <section class="project" id="item3">this is section 3</section>
</div>

<footer class="endings">
 <h1>some text</h1>
</footer>

我附加了一些样式来模拟现实情况。

这里是javascript逻辑:

获取所有项目:

const projects = Array.from(document.querySelectorAll('.project'));

获取所有项目距顶部的偏移量和所有项目的高度:

let projectsOffsetTop = projects.map(project => project.offsetTop);
let projectsHeight = projects.map(project => project.offsetHeight);

创建一个函数来在有人调整窗口大小时更新值:

function updateProjectsOffsetTop() {
  projectsOffsetTop = projects.map(project => project.offsetTop);
  projectsHeight = projects.map(project => project.offsetHeight);
};

window.addEventListener('resize', updateProjectsOffsetTop);

如果滚动大于其偏移量，则最终固定元素。

function pinElement() {

  if (window.scrollY >= projectsOffsetTop[1]) {
    document.body.style.paddingTop = projectsHeight[1] +'px';
    projects[1].classList.add('fixed');
  } else {
    document.body.style.paddingTop = 0;
    projects[1].classList.remove('fixed');
  }

};

window.addEventListener('scroll', pinElement);

但我无法让它与所有项目元素一起使用。即使有 for 循环。最佳做法是什么？如果可能的话，我想在 Vanilla ES6 中解决这个问题。

在附件中找到完整的 js fiddle。

谢谢

const projects = Array.from(document.querySelectorAll('.project'));
    let projectsOffsetTop = projects.map(project => project.offsetTop);
    let projectsHeight = projects.map(project => project.offsetHeight);

    function updateProjectsOffsetTop() {
      projectsOffsetTop = projects.map(project => project.offsetTop);
      projectsHeight = projects.map(project => project.offsetHeight);
    };

    function pinElement() {

      if (window.scrollY >= projectsOffsetTop[1]) {
        document.body.style.paddingTop = projectsHeight[1] +'px';
        projects[1].classList.add('fixed');
      } else {
        document.body.style.paddingTop = 0;
        projects[1].classList.remove('fixed');
      }

    };

    window.addEventListener('resize', updateProjectsOffsetTop);
    window.addEventListener('scroll', pinElement);

html {
      box-sizing: border-box;
      
    }

    *, *::before, *::after {
      box-sizing: inherit;
      margin: 0;
      padding: 0;
    }

    header, footer {
      width: 100%;
      padding: 10%;
      background-color: grey;
      position: relative;
    }

    .project {
      width: 100%;
      height: 100vh;
      position: relative;
      display: flex;
      justify-content: center;
      align-items: center;
      top: 0;
    }

    #item1 {background-color: yellow;}
    #item2 {background-color: blue;}
    #item3 {background-color: red;}


    .fixed {
      position: fixed;
    }

<header class="forewords"><h1>Lorem ipsum dolor sit amet, consectetur adipisicing elit. Harum soluta ipsam quaerat cupiditate neque, necessitatibus amet nihil perferendis sunt minus! Exercitationem nulla inventore, aut beatae magnam, totam et minus hic.</h1>
  </header>

  <div class="wrapper">
    <section class="project" id="item1">this is section 1</section>
    <section class="project" id="item2">this is section 2</section>
    <section class="project" id="item3">this is section 3</section>
  </div>

  <footer class="endings"><h1>Lorem ipsum dolor sit amet, consectetur adipisicing elit. Repudiandae vel, perferendis ullam totam recusandae sed repellendus cum! Molestiae, aut ut sequi eos quidem nam quo est, ad tempora inventore odit.</h1>
  </footer>

Answer 1

您提供了令人惊叹的 MCVE 工作，非常感谢您花费如此多的精力和时间来提出一个很好的问题。好消息是您快了!你的逻辑是合理的，一切都是有道理的。你真正缺少的是:

• 重置样式的逻辑的正确位置(body 顶部填充和删除 fixed 类)
• 获取最接近但大于滚动高度的 .project 元素的索引

您想在 pinElement() 方法中执行的操作如下:

1. 首先重置/解除一切
2. 获取大于 scrollY 但最接近它的 projectsOffsetTop 值(这样它将成为我们要固定的元素)
3. 从中获取该值所属的 .project 元素的索引
4. 如果索引为-1(即我们没有符合第 2 点条件的元素)，返回并停止执行。
5. 否则，我们将执行您在原始方法中的逻辑，但将 1 替换为我们在第 3 步中确定的索引。

考虑到这一点，这里是您稍微重构的 pinElement() 方法:

function pinElement() {

  // Reset all styles
  projects.forEach((project) => {
    document.body.style.paddingTop = 0;
    project.classList.remove('fixed');
  });

  // Get the index of the project that is closest to top
  const valueClosestToScrollY = Math.max.apply(Math, projectsOffsetTop.filter((offsetTop) => offsetTop <= window.scrollY));
  const idx = projectsOffsetTop.indexOf(valueClosestToScrollY);

  // If index is not found, we don't do anything
  if (idx === -1)
    return;

  // Otherwise, we set the appropriate styles and classes
  if (window.scrollY >= projectsOffsetTop[idx]) {
    document.body.style.paddingTop = `${projectsHeight[idx]}px`;
    projects[idx].classList.add('fixed');
  }

};

有趣的提示:您可以使用模板文字来做到这一点:

document.body.style.paddingTop = `${projectsHeight[idx]}px`;

...而不是这个:

document.body.style.paddingTop = ${projectsHeight[idx] + 'px';

这是一个概念验证示例:

const projects = Array.from(document.querySelectorAll('.project'));
let projectsOffsetTop = projects.map(project => project.offsetTop);
let projectsHeight = projects.map(project => project.offsetHeight);

function updateProjectsOffsetTop() {
  projectsOffsetTop = projects.map(project => project.offsetTop);
  projectsHeight = projects.map(project => project.offsetHeight);
};

function pinElement() {

  // Reset all styles
  projects.forEach((project) => {
    document.body.style.paddingTop = 0;
    project.classList.remove('fixed');
  });

  // Get the index of the project that is closest to top
  const valueClosestToScrollY = Math.max.apply(Math, projectsOffsetTop.filter((offsetTop) => offsetTop <= window.scrollY));
  const idx = projectsOffsetTop.indexOf(valueClosestToScrollY);
  
  // If index is not found, we don't do anything
  if (idx === -1)
    return;

  // Otherwise, we set the appropriate styles and classes
  if (window.scrollY >= projectsOffsetTop[idx]) {
    document.body.style.paddingTop = `${projectsHeight[idx]}px`;
    projects[idx].classList.add('fixed');
  }

};

window.addEventListener('resize', updateProjectsOffsetTop);
window.addEventListener('scroll', pinElement);

html {
  box-sizing: border-box;
}

*,
*::before,
*::after {
  box-sizing: inherit;
  margin: 0;
  padding: 0;
}

header,
footer {
  width: 100%;
  padding: 10%;
  background-color: grey;
  position: relative;
}

.project {
  width: 100%;
  height: 100vh;
  position: relative;
  display: flex;
  justify-content: center;
  align-items: center;
  top: 0;
}

#item1 {
  background-color: yellow;
}

#item2 {
  background-color: blue;
}

#item3 {
  background-color: red;
}

.fixed {
  position: fixed;
}

<header class="forewords">
  <h1>Lorem ipsum dolor sit amet, consectetur adipisicing elit. Harum soluta ipsam quaerat cupiditate neque, necessitatibus amet nihil perferendis sunt minus! Exercitationem nulla inventore, aut beatae magnam, totam et minus hic.</h1>
</header>

<div class="wrapper">
  <section class="project" id="item1">this is section 1</section>
  <section class="project" id="item2">this is section 2</section>
  <section class="project" id="item3">this is section 3</section>
</div>

<footer class="endings">
  <h1>Lorem ipsum dolor sit amet, consectetur adipisicing elit. Repudiandae vel, perferendis ullam totam recusandae sed repellendus cum! Molestiae, aut ut sequi eos quidem nam quo est, ad tempora inventore odit.</h1>
</footer>

---

附带说明一下，出于性能原因，您可能需要研究对滚动事件进行节流/去抖动，以免过度调用 pinElement()。