Vanilla Javascript 切换下拉菜单答案

【问题标题】：Vanilla Javascript Toggle Drop Down MenuVanilla Javascript 切换下拉菜单
【发布时间】：2018-06-09 13:47:16
【问题描述】：

我的大脑已经检查了周末......

我正在寻找一个纯 Javascript 的解决方案，如果在单击另一个主菜单项时打开一个下拉菜单框，则先前打开的下拉菜单将关闭，然后显示新单击的主菜单项的下拉菜单。我知道这可能很简单，但我想不出一个不复杂的解决方案。

此外，如果您在菜单项之外（文档上不是菜单项或下拉框的任何位置）单击，则应关闭所有打开的下拉菜单。

感谢您的帮助。

function testFunc(el) {
  var parent = el.parentElement;
  var dd = parent.lastChild.previousSibling;
  dd.classList.toggle('show');
}

ul { list-style: none; margin: 0; padding: 0; }
ul li {
  width: 100px;
  float: left;
  background: #dbdbdb;
  line-height: 2em;
  text-align: center;
  margin: 0 5px;
  cursor: pointer;
}
ul li span {
  display: block;
}
ul li ul {
  display: none;
}

.show {
  display: block;
}

<ul>
  <li>
    <span onclick="testFunc(this)">Item 1</span>
    <ul>
      <li>Sub Item 1</li>
      <li>Sub Item 2</li>
    </ul>
  </li>
  <li>
    <span onclick="testFunc(this)">Item 2</span>
    <ul>
      <li>Sub Item 1</li>
      <li>Sub Item 2</li>
    </ul>
  </li>
  <li>
    <span onclick="testFunc(this)">Item 3</span>
    <ul>
      <li>Sub Item 1</li>
      <li>Sub Item 2</li>
    </ul>
  </li>
  <li>
    <span onclick="testFunc(this)">Item 4</span>
    <ul>
      <li>Sub Item 1</li>
      <li>Sub Item 2</li>
    </ul>
  </li>
</ul>

【问题讨论】：

标签： javascript navigation toggle

【解决方案1】：

切换菜单可见性

您可以将上次打开的菜单保存在函数外部的变量opened 中。然后，当单击菜单时，如果 opened 不是 null，它将切换 opened（即隐藏最后打开的菜单）并切换单击的项目。

let opened = null

function testFunc(el) {

  // gets the <ul> element of the clicked menu item
  const menu = el.parentElement.lastChild.previousSibling;

  if (!opened) {

    // no menu item is shown
    opened = menu
    opened.classList.toggle('show');

  } else if (menu == opened) {

    // the clicked item is already showing
    menu.classList.toggle('show')
    opened = null

  } else {

    // the clicked item is hiddden but another one is showing
    opened.classList.toggle('show')
    opened = menu
    opened.classList.toggle('show')

  }

}

代码如下：

let opened = null

function testFunc(el) {

  const menu =  el.parentElement.lastChild.previousSibling;
  
  if(!opened) {
    opened = menu
    opened.classList.toggle('show');
  } else if(menu == opened) {
    menu.classList.toggle('show')
    opened = null
  } else {
    opened.classList.toggle('show')
    opened = menu
    opened.classList.toggle('show')
  }
  
}

ul {
  list-style: none;
  margin: 0;
  padding: 0;
}

ul li {
  width: 100px;
  float: left;
  background: #dbdbdb;
  line-height: 2em;
  text-align: center;
  margin: 0 5px;
  cursor: pointer;
}

ul li span {
  display: block;
}

ul li ul {
  display: none;
}

.show {
  display: block;
}

<ul>
  <li>
    <span onclick="testFunc(this)">Item 1</span>
    <ul>
      <li>Sub Item 1</li>
      <li>Sub Item 2</li>
    </ul>
  </li>
  <li>
    <span onclick="testFunc(this)">Item 2</span>
    <ul>
      <li>Sub Item 1</li>
      <li>Sub Item 2</li>
    </ul>
  </li>
  <li>
    <span onclick="testFunc(this)">Item 3</span>
    <ul>
      <li>Sub Item 1</li>
      <li>Sub Item 2</li>
    </ul>
  </li>
  <li>
    <span onclick="testFunc(this)">Item 4</span>
    <ul>
      <li>Sub Item 1</li>
      <li>Sub Item 2</li>
    </ul>
  </li>
</ul>

ES6 语法的变体

这是一个带有一些 ES6 语法的变体，注意我已经更改了 HTML 命名结构以更好地维护代码，允许通过类名调用元素

不必使用内联事件侦听器
在一行中调用所有菜单项

这里是 JavaScript 代码：

let opened = null
const toggleVisibility = e => e.classList.toggle('show')

const toggleDropDown = e => {

  const clickedItem = e.target.parentElement.lastChild.previousSibling

  toggleVisibility(clickedItem);

  if (!opened) {
    opened = clickedItem
  } else if (opened == clickedItem) {
    opened = null
  } else {
    toggleVisibility(opened);
    opened = clickedItem
  }

}

[...document.querySelectorAll('.dropDown')].forEach(dropDown => dropDown.addEventListener('click', toggleDropDown))

let opened = null
const toggleVisibility = e => e.classList.toggle('show')

const toggleDropDown = e => {

  const clickedItem = e.target.parentElement.lastChild.previousSibling

  toggleVisibility(clickedItem);

  if (!opened) {
    opened = clickedItem
  } else if (opened == clickedItem) {
    opened = null
  } else {
    toggleVisibility(opened);
    opened = clickedItem
  }

}

[...document.querySelectorAll('.dropDown')].forEach(dropDown => dropDown.addEventListener('click', toggleDropDown))

ul {
  list-style: none;
  margin: 0;
  padding: 0;
}

ul li {
  width: 100px;
  float: left;
  background: #dbdbdb;
  line-height: 2em;
  text-align: center;
  margin: 0 5px;
  cursor: pointer;
}

ul li span {
  display: block;
}

ul li ul {
  display: none;
}

.show {
  display: block;
}

<ul>
  <li>
    <span class="dropDown">Item 1</span>
    <ul>
      <li>Sub Item 1</li>
      <li>Sub Item 2</li>
    </ul>
  </li>
  <li>
    <span class="dropDown">Item 2</span>
    <ul>
      <li>Sub Item 1</li>
      <li>Sub Item 2</li>
    </ul>
  </li>
  <li>
    <span class="dropDown">Item 3</span>
    <ul>
      <li>Sub Item 1</li>
      <li>Sub Item 2</li>
    </ul>
  </li>
  <li>
    <span class="dropDown">Item 4</span>
    <ul>
      <li>Sub Item 1</li>
      <li>Sub Item 2</li>
    </ul>
  </li>
</ul>

点击其他地方时切换菜单可见性 + 关闭

如果您想在用户在菜单外单击时关闭任何打开的菜单，您需要在文档本身上有一个事件监听器。因此，不是每个菜单按钮都有一个事件侦听器，而是只有一个事件侦听器来监视文档中发生的任何点击。

事件监听器将判断点击的项目是否是一个菜单按钮，在这种情况下，它将运行菜单处理程序。否则它将关闭最后打开的菜单项。

JavaScript 代码：

let opened = null
const toggleVisibility = e => e.classList.toggle('show')

const handleDropdown = e => {

  const clickedItem = e.parentElement.lastChild.previousSibling

  toggleVisibility(clickedItem)

  if (!opened) {
    opened = clickedItem
  } else if (opened == clickedItem) {
    opened = null
  } else {
    toggleVisibility(opened)
    opened = clickedItem
  }

}

const handleClick = e => {

  if (e.target.className.includes('dropDown')) {
    handleDropdown(e.target)
  } else if (opened) {
    toggleVisibility(opened)
    opened = null
  }

}

document.addEventListener('click', handleClick)

这里是完整的代码：

let opened = null
const toggleVisibility = e => e.classList.toggle('show')

const handleDropdown = e => {

  const clickedItem = e.parentElement.lastChild.previousSibling

  toggleVisibility(clickedItem)

  if (!opened) {
    opened = clickedItem
  } else if (opened == clickedItem) {
    opened = null
  } else {
    toggleVisibility(opened)
    opened = clickedItem
  }

}

const handleClick = e => {

  if (e.target.className.includes('dropDown')) {
    handleDropdown(e.target)
  } else if (opened) {
    toggleVisibility(opened)
    opened = null
  }

}

document.addEventListener('click', handleClick)

ul {
  list-style: none;
  margin: 0;
  padding: 0;
}

ul li {
  width: 100px;
  float: left;
  background: #dbdbdb;
  line-height: 2em;
  text-align: center;
  margin: 0 5px;
  cursor: pointer;
}

ul li span {
  display: block;
}

ul li ul {
  display: none;
}

.show {
  display: block;
}

<ul>
  <li>
    <span class="dropDown">Item 1</span>
    <ul>
      <li>Sub Item 1</li>
      <li>Sub Item 2</li>
    </ul>
  </li>
  <li>
    <span class="dropDown">Item 2</span>
    <ul>
      <li>Sub Item 1</li>
      <li>Sub Item 2</li>
    </ul>
  </li>
  <li>
    <span class="dropDown">Item 3</span>
    <ul>
      <li>Sub Item 1</li>
      <li>Sub Item 2</li>
    </ul>
  </li>
  <li>
    <span class="dropDown">Item 4</span>
    <ul>
      <li>Sub Item 1</li>
      <li>Sub Item 2</li>
    </ul>
  </li>
</ul>

【讨论】：

真棒伊万。但正如 31piy 所提到的，实际的切换功能不再起作用。如果保留父级的切换功能但在顶部添加新功能，那将是理想的。
@Ivan 完美！太感谢了！如果在菜单项之外（文档上不是菜单项或下拉框的任何地方）单击关闭任何打开的下拉菜单，有什么想法吗？
我已将第三部分添加到我的答案中。它实际上是一种更有效的处理鼠标点击的方法：有一个事件监听器（与第一个版本相比，每个菜单项添加一个）
伟大的伊万！完美运行……比我最初处理如此看似简单的任务所需的代码少得多。谢谢我的兄弟！

【解决方案2】：

很难与 Ivan 的答案竞争，但这将是我使用 ES6 语法对同一问题的解决方案：

class Dropdown {

  constructor() {
    this.listen();
  }

  // Listen to ALL (!) click events to also catch clicks OUTSIDE the dropdowns
  listen() {
    document.addEventListener('click', (e) => {
      if (e.target.classList.contains('dropdown')) {
        this.closeOthers(e.target);
        this.handleClick(e.target);
      } else {
        this.closeOthers(null);
      }
    });
  }

  // Add or remove 'expanded' CSS class, depending on the current situation
  handleClick(dropdown) {
    if (dropdown.classList.contains('expanded')) {
      dropdown.classList.remove('expanded');
    } else {
      dropdown.classList.add('expanded');
    }
  }

  // Close all dropdowns except the one that gets passed as the element parameter
  // Note that we may also pass null in order to close ALL dropdowns
  closeOthers(element) {
    document.querySelectorAll('.dropdown').forEach((dropdown) => {
      if (element != dropdown) {
        dropdown.classList.remove('expanded');
      }
    });
  }

}

document.addEventListener('DOMContentLoaded', () => new Dropdown);

它对我有用。不确定它是否适用于其他人。感谢您的反馈。

【讨论】：