Add Class to Element Javascript

<script type="module" src="https://unpkg.com/ionicons@7.1.0/dist/ionicons/ionicons.esm.js"></script>
<script nomodule src="https://unpkg.com/ionicons@7.1.0/dist/ionicons/ionicons.js"></script>

<div class="container">
  <h1>Add Class to Element</h1>
  <p class="subtitle">Interactive JavaScript Class Manipulation Demo</p>

  <div class="demo-section">
    <h2>
      <ion-icon name="cube-outline"></ion-icon>
      Basic Example
    </h2>
    <div class="demo-box" id="box1">
      <p>Click the button to add a highlight class!</p>
      <span class="status status-inactive" id="status1">Not Highlighted</span>
    </div>
    <div class="btn-group">
      <button class="btn" id="addBtn1">
        <ion-icon name="add-circle-outline"></ion-icon>
        Add Class
      </button>
      <button class="btn btn-secondary" id="removeBtn1">
        <ion-icon name="remove-circle-outline"></ion-icon>
        Remove Class
      </button>
      <button class="btn btn-secondary" id="toggleBtn1">
        <ion-icon name="repeat-outline"></ion-icon>
        Toggle Class
      </button>
    </div>
  </div>

  <div class="info-box">
    <h3>
      <ion-icon name="code-slash-outline"></ion-icon>
      Code Example
    </h3>
    <div class="code-block">
      <span class="comment">// Add a single class</span>
      element.<span class="keyword">classList</span>.<span class="keyword">add</span>(<span class="string">'highlight'</span>);

      <span class="comment">// Remove a class</span>
      element.<span class="keyword">classList</span>.<span class="keyword">remove</span>(<span class="string">'highlight'</span>);

      <span class="comment">// Toggle a class</span>
      element.<span class="keyword">classList</span>.<span class="keyword">toggle</span>(<span class="string">'highlight'</span>);

      <span class="comment">// Add multiple classes</span>
      element.<span class="keyword">classList</span>.<span class="keyword">add</span>(<span class="string">'class1'</span>, <span class="string">'class2'</span>, <span class="string">'class3'</span>);

      <span class="comment">// Check if class exists</span>
      <span class="keyword">if</span> (element.<span class="keyword">classList</span>.<span class="keyword">contains</span>(<span class="string">'highlight'</span>)) {
      console.log(<span class="string">'Class exists!'</span>);
      }
    </div>
  </div>

  <div class="demo-section">
    <h2>
      <ion-icon name="layers-outline"></ion-icon>
      Multiple Classes
    </h2>
    <div class="demo-box" id="box2">
      <p>Add multiple classes at once!</p>
    </div>
    <div class="btn-group">
      <button class="btn" id="addBordered">
        <ion-icon name="square-outline"></ion-icon>
        Add Border
      </button>
      <button class="btn" id="addRounded">
        <ion-icon name="ellipse-outline"></ion-icon>
        Add Rounded
      </button>
      <button class="btn" id="addShadow">
        <ion-icon name="contrast-outline"></ion-icon>
        Add Shadow
      </button>
      <button class="btn btn-secondary" id="addAll">
        <ion-icon name="star-outline"></ion-icon>
        Add All
      </button>
      <button class="btn btn-secondary" id="removeAll">
        <ion-icon name="trash-outline"></ion-icon>
        Remove All
      </button>
    </div>
  </div>

  <div class="demo-section">
    <h2>
      <ion-icon name="grid-outline"></ion-icon>
      Toggle Multiple Elements
    </h2>
    <div class="multi-demo">
      <div class="small-box" data-box="1">Box 1</div>
      <div class="small-box" data-box="2">Box 2</div>
      <div class="small-box" data-box="3">Box 3</div>
      <div class="small-box" data-box="4">Box 4</div>
    </div>
    <p style="text-align: center; margin-top: 15px; color: #666; font-size: 14px;">
      Click on any box to toggle its active state
    </p>
  </div>

  <div class="info-box">
    <h3>
      <ion-icon name="information-circle-outline"></ion-icon>
      Key Methods
    </h3>
    <ul>
      <li><strong>classList.add()</strong> - Adds one or more classes to an element</li>
      <li><strong>classList.remove()</strong> - Removes one or more classes from an element</li>
      <li><strong>classList.toggle()</strong> - Toggles a class on/off</li>
      <li><strong>classList.contains()</strong> - Checks if element has a specific class</li>
      <li><strong>classList.replace()</strong> - Replaces an existing class with a new one</li>
    </ul>
  </div>
</div>

       * {
            margin: 0;
            padding: 0;
            box-sizing: border-box;
        }

        body {
            font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Oxygen, Ubuntu, Cantarell, sans-serif;
            background: linear-gradient(135deg, #ff6b6b 0%, #ee5a6f 50%, #c44569 100%);
            min-height: 100vh;
            display: flex;
            align-items: center;
            justify-content: center;
            padding: 20px;
        }

        .container {
            background: white;
            border-radius: 20px;
            box-shadow: 0 20px 60px rgba(0, 0, 0, 0.3);
            padding: 50px 40px;
            width: 100%;
            max-width: 700px;
        }

        h1 {
            font-size: 32px;
            color: #333;
            margin-bottom: 10px;
            font-weight: 600;
            text-align: center;
        }

        .subtitle {
            color: #666;
            font-size: 15px;
            margin-bottom: 40px;
            text-align: center;
        }

        .demo-section {
            background: #f8f9fa;
            border-radius: 12px;
            padding: 30px;
            margin-bottom: 30px;
        }

        .demo-section h2 {
            font-size: 20px;
            color: #ff6b6b;
            margin-bottom: 20px;
            display: flex;
            align-items: center;
            gap: 10px;
        }

        .demo-box {
            background: white;
            border: 2px dashed #ddd;
            border-radius: 12px;
            padding: 30px;
            text-align: center;
            margin-bottom: 20px;
            transition: all 0.4s ease;
        }

        .demo-box p {
            color: #666;
            font-size: 16px;
            margin-bottom: 10px;
        }

        /* Classes to be added dynamically */
        .highlight {
            background: linear-gradient(135deg, #ff6b6b 0%, #ee5a6f 100%);
            color: white;
            border-color: #ff6b6b;
            transform: scale(1.05);
            box-shadow: 0 10px 30px rgba(255, 107, 107, 0.3);
        }

        .highlight p {
            color: white;
        }

        .bordered {
            border: 3px solid #ff6b6b;
            border-style: solid;
        }

        .rounded {
            border-radius: 50px;
        }

        .shadow {
            box-shadow: 0 15px 40px rgba(0, 0, 0, 0.2);
        }

        .animated {
            animation: bounce 0.6s ease;
        }

        @keyframes bounce {
            0%, 100% { transform: translateY(0); }
            25% { transform: translateY(-10px); }
            50% { transform: translateY(0); }
            75% { transform: translateY(-5px); }
        }

        .btn {
            background: linear-gradient(135deg, #ff6b6b 0%, #ee5a6f 100%);
            color: white;
            border: none;
            border-radius: 10px;
            padding: 12px 24px;
            font-size: 15px;
            font-weight: 600;
            cursor: pointer;
            transition: all 0.3s ease;
            display: inline-flex;
            align-items: center;
            gap: 8px;
            margin: 5px;
        }

        .btn:hover {
            transform: translateY(-2px);
            box-shadow: 0 8px 20px rgba(255, 107, 107, 0.4);
        }

        .btn:active {
            transform: translateY(0);
        }

        .btn-secondary {
            background: linear-gradient(135deg, #95a5a6 0%, #7f8c8d 100%);
        }

        .btn-group {
            display: flex;
            flex-wrap: wrap;
            gap: 10px;
            justify-content: center;
        }

        .code-block {
            background: #2d2d2d;
            color: #f8f8f2;
            padding: 20px;
            border-radius: 10px;
            font-family: 'Courier New', monospace;
            font-size: 14px;
            overflow-x: auto;
            margin: 20px 0;
            line-height: 1.6;
        }

        .code-block .keyword {
            color: #ff79c6;
        }

        .code-block .string {
            color: #f1fa8c;
        }

        .code-block .comment {
            color: #6272a4;
        }

        .info-box {
            background: #fff5f5;
            border-left: 4px solid #ff6b6b;
            padding: 20px;
            border-radius: 8px;
            margin: 20px 0;
        }

        .info-box h3 {
            color: #ff6b6b;
            margin-bottom: 10px;
            font-size: 18px;
            display: flex;
            align-items: center;
            gap: 8px;
        }

        .info-box ul {
            margin-left: 20px;
            color: #555;
        }

        .info-box li {
            margin: 8px 0;
        }

        .status {
            display: inline-block;
            padding: 6px 12px;
            border-radius: 20px;
            font-size: 13px;
            font-weight: 600;
            margin-top: 10px;
        }

        .status-active {
            background: #d4edda;
            color: #155724;
        }

        .status-inactive {
            background: #f8d7da;
            color: #721c24;
        }

        .multi-demo {
            display: grid;
            grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
            gap: 20px;
            margin-top: 20px;
        }

        .small-box {
            background: white;
            border: 2px solid #ddd;
            border-radius: 10px;
            padding: 20px;
            text-align: center;
            transition: all 0.3s ease;
            cursor: pointer;
        }

        .small-box:hover {
            border-color: #ff6b6b;
        }

        .small-box.active {
            background: linear-gradient(135deg, #ff6b6b 0%, #ee5a6f 100%);
            color: white;
            border-color: #ff6b6b;
            transform: scale(1.05);
        }

     // Basic Example
        const box1 = document.getElementById('box1');
        const status1 = document.getElementById('status1');
        const addBtn1 = document.getElementById('addBtn1');
        const removeBtn1 = document.getElementById('removeBtn1');
        const toggleBtn1 = document.getElementById('toggleBtn1');

        function updateStatus() {
            if (box1.classList.contains('highlight')) {
                status1.textContent = 'Highlighted';
                status1.className = 'status status-active';
            } else {
                status1.textContent = 'Not Highlighted';
                status1.className = 'status status-inactive';
            }
        }

        addBtn1.addEventListener('click', () => {
            box1.classList.add('highlight');
            updateStatus();
        });

        removeBtn1.addEventListener('click', () => {
            box1.classList.remove('highlight');
            updateStatus();
        });

        toggleBtn1.addEventListener('click', () => {
            box1.classList.toggle('highlight');
            updateStatus();
        });

        // Multiple Classes Example
        const box2 = document.getElementById('box2');
        const addBordered = document.getElementById('addBordered');
        const addRounded = document.getElementById('addRounded');
        const addShadow = document.getElementById('addShadow');
        const addAll = document.getElementById('addAll');
        const removeAll = document.getElementById('removeAll');

        addBordered.addEventListener('click', () => {
            box2.classList.add('bordered');
        });

        addRounded.addEventListener('click', () => {
            box2.classList.add('rounded');
        });

        addShadow.addEventListener('click', () => {
            box2.classList.add('shadow');
        });

        addAll.addEventListener('click', () => {
            box2.classList.add('bordered', 'rounded', 'shadow', 'animated');
        });

        removeAll.addEventListener('click', () => {
            box2.classList.remove('bordered', 'rounded', 'shadow', 'animated');
        });

        // Multiple Elements Example
        const smallBoxes = document.querySelectorAll('.small-box');

        smallBoxes.forEach(box => {
            box.addEventListener('click', () => {
                box.classList.toggle('active');
            });
        });