ハンバーガーメニューの完全なコードはこちらから。

ハンバーガーメニューを自作するのが面倒な人へ捧ぐ。

HTML
```html
<!DOCTYPE html>
<html lang="ja">
  <head>
    <meta charset="UTF-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>hamburger practice</title>
    <link rel="stylesheet" href="./style.css" />
  </head>
  <body>
    <nav class="nav">
      <button class="hamburger">
        <span></span>
        <span></span>
        <span></span>
      </button>
      <div class="menu">
        <ul>
          <li><a href="#home">Home</a></li>
          <li><a href="#about">About us</a></li>
          <li><a href="#service">Service</a></li>
          <li><a href="#contact">Contact</a></li>
        </ul>
      </div>
    </nav>

    <script src="./script.js"></script>
  </body>
</html>

```

CSS
```css
/* リセットCSS */
* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}

.nav {
  position: fixed;
  top: 0;
  left: 0;
  width: 100%;
  padding: 1rem;
  background-color: #fff;
  box-shadow: 0 2px 5px rgba(0, 0, 0, 0.1);
}

.hamburger {
  position: relative;
  width: 30px;
  height: 24px;
  cursor: pointer;
  z-index: 100;
  border: none;
  background: none;
}

.hamburger span {
  position: absolute;
  left: 0;
  width: 100%;
  height: 2px;
  background-color: #333;
  transition: all 0.4s;
}

.hamburger span:nth-child(1) {
  top: 0;
}

.hamburger span:nth-child(2) {
  top: 11px;
}

.hamburger span:nth-child(3) {
  bottom: 0;
}

.hamburger.active span:nth-child(1) {
  transform: translateY(11px) rotate(-45deg);
  background-color: #fff;
}

.hamburger.active span:nth-child(2) {
  opacity: 0;
  background-color: #fff;
}

.hamburger.active span:nth-child(3) {
  transform: translateY(-11px) rotate(45deg);
  background-color: #fff;
}

.menu {
  position: fixed;
  top: 0;
  left: 0;
  width: 100%;
  height: 100vh;
  background-color: rgba(0,0,0,0.9);
  color: #fff;
  display: flex;
  flex-direction: column;
  justify-content: center;
  align-items: center;
  transform: translateX(100%);
  transition: transform 0.4s;
}

.menu.active {
  transform: translateX(0);
}

.menu ul {
  list-style: none;
}

.menu li {
  margin: 1.5rem 0;
  font-size: 1.5rem;
  opacity: 0;
  transform: translateX(20px);
  transition: all 0.4s;
}

.menu.active li {
  opacity: 1;
  transform: translateX(0);
}

/* メニュー項目の遅延アニメーション */
.menu.active li:nth-child(1) { transition-delay: 0.2s; }
.menu.active li:nth-child(2) { transition-delay: 0.3s; }
.menu.active li:nth-child(3) { transition-delay: 0.4s; }
.menu.active li:nth-child(4) { transition-delay: 0.5s; }

/* メニューリンク */
.menu a {
  color: #fff;
  text-decoration: none;
  position: relative;
}

.menu a::after {
  content: '';
  position: absolute;
  bottom: -4px;
  left: 0;
  width: 100%;
  height: 2px;
  background-color: #fff;
  transform: scaleX(0);
  transition: transform 0.3s;
  transform-origin: right;
}

.menu a:hover::after {
  transform: scaleX(1);
  transform-origin: left;
}
```

JavaScript
```javascript
const hamburger = document.querySelector(".hamburger");
const menu = document.querySelector(".menu");

hamburger.addEventListener("click", () => {
  hamburger.classList.toggle("active");
  menu.classList.toggle("active");
});

document.querySelectorAll(".menu a").forEach((link) => {
  link.addEventListener("click", () => {
    hamburger.classList.remove("active");
    menu.classList.remove("active");
  });
});

document.addEventListener("click", (e) => {
  if (!hamburger.contains(e.target) && !menu.contains(e.target)) {
    hamburger.classList.remove("active");
    menu.classList.remove("active");
  }
});
```