使用原生 JavaScript 实现响应式多级下拉菜单（悬停与点击）

<li>
    <span class="menu--item">Link</span>
    <ul class="children">
        <li>Child Link</li>
        <li>Child Link</li>
    </ul>
</li>

.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);
  });
}