使用纯 JavaScript 实现响应式多级下拉菜单：悬停与点击的结合

<div class="menu">
  <ul>
    <li>
      Parent 1
      <ul>
        <li class="link">
          <a href="">Child 1</a>
        </li>
        <li class="link">
          <a href="">Child 2</a>
        </li>
        <li>
          Nested child
          <ul>
            <li class="link">
              <a href="">Something</a>
            </li>
            <li class="link">
              <a href="">Something</a>
            </li>
          </ul>
        </li>
      </ul>
    </li>
    <li>
      Parent 2
      <ul>
        <li class="link">
          <a href="">Basic link 1</a>
        </li>
        <li class="link">
          <a href="">Basic link 2</a>
        </li>
        <li>
          Nested child 2
          <ul>
            <li class="link">
              <a href="">Basic nested link 1</a>
            </li>
            <li class="link">
              <a href="">Basic nested link 2</a>
            </li>

          </ul>
        </li>
      </ul>
    </li>
    <li class="link">Simple Link</li>
    <li class="link">Another Link</li>
  </ul>
</div>

.menu {
  --menu-height: 40px;
  box-sizing: border-box;
  position: fixed;
  top: 0;
  left: 0;
  width: 100vw;
}
.menu ul {
  list-style: none;
  padding: 16px;
  margin: 0;
}
.menu ul li,
.menu ul li a {
  opacity: 0.8;
  color: #ffffff;
  cursor: pointer;
  transition: 200ms;
  text-decoration: none;
  white-space: nowrap;
  font-weight: 700;
}
.menu ul li a,
.menu ul li a a {
  display: flex;
  align-items: center;
  height: 100%;
  width: 100%;
}
.menu ul li {
  padding-right: 36px;
}
.menu ul li::before {
  content: "";
  width: 0;
  height: 0;
  border-left: 5px solid transparent;
  border-right: 5px solid transparent;
  border-top: 5px solid #ffa500;
  position: absolute;
  right: 8px;
  top: 50%;
  transform: translateY(-50%);
}
.menu ul .link::before {
  padding-right: 0;
  display: none;
}
.menu > ul {
  display: flex;
  height: var(--menu-height);
  align-items: center;
  background-color: #000000;
}
.menu > ul li {
  position: relative;
  margin: 0 8px;
}
.menu > ul li ul {
  visibility: hidden;
  opacity: 0;
  padding: 0;
  min-width: 160px;
  background-color: #333;
  position: absolute;
  top: 45px;
  left: 50%;
  transform: translateX(-50%);
  transition: 200ms;
  transition-delay: 200ms;
}
.menu > ul li ul li {
  margin: 0;
  padding: 8px 16px;
  display: flex;
  align-items: center;
  justify-content: flex-start;
  height: 30px;
  padding-right: 40px;
}
.menu > ul li ul li::before {
  width: 0;
  height: 0;
  border-top: 5px solid transparent;
  border-bottom: 5px solid transparent;
  border-left: 5px solid #ffa500;
}
.menu > ul li ul li ul {
  top: -2%;
  left: 100%;
  transform: translate(0);
}

.show {
  display: flex;
}

.hide {
  display: none;
}

@media screen and (min-width: 1200px) {
  .menu ul li:hover,
  .menu ul li a:hover {
    opacity: 1;
  }
  .menu > ul li ul li:hover {
    background: black;
  }
  .menu > ul li:hover > ul {
    opacity: 1;
    visibility: visible;
    transition-delay: 0ms;
  }
}

@media screen and (max-width: 1200px) {
  .menu {
    height: 100vh;
    top: 0;
    left: 0;
    width: 20vw;
  }
  .menu ul {
    flex-direction: column;
    height: 100vh;
  }
  .menu ul li {
    margin: 1rem 0;
  }
  .menu ul li ul {
    visibility: hidden;
    opacity: 0;
    padding: 0;
    min-width: 160px;
    background-color: #333;
    position: absolute;
    top: 0px;
    left: 200%;
    transform: translateX(-50%);
    transition: 200ms;
    transition-delay: 200ms;
    height: fit-content;
  }

  .menu ul.show {
    visibility: visible;
    opacity: 1;
  }
}

let menu = document.querySelector(".menu ul");
menu = menu.children;

for (let i = 0; i < menu.length; i++) {
  console.log(menu[i]);
  menu[i].addEventListener("click", function() {
    menu[i].firstElementChild.classList.toggle("show");
    console.log(menu[i].firstElementChild);
  });
}

document.addEventListener('DOMContentLoaded', function() {
  const menuItems = document.querySelectorAll('.menu ul li');
  const mediaQuery = window.matchMedia('(max-width: 1200px)');

  function handleMenuItemClick(event) {
    // 阻止事件冒泡，防止父元素同时触发
    event.stopPropagation();

    const subMenu = this.querySelector('ul');
    if (subMenu) {
      subMenu.classList.toggle('show');
    }
  }

  function attachEventListeners(matches) {
    menuItems.forEach(item => {
      item.removeEventListener('click', handleMenuItemClick); // 移除之前的监听器

      if (matches) {
        item.addEventListener('click', handleMenuItemClick);
      }
    });
  }

  // 初始化时执行一次
  attachEventListeners(mediaQuery.matches);

  // 监听媒体查询变化
  mediaQuery.addEventListener('change', (event) => {
    attachEventListeners(event.matches);
  });
});