Displays a slideshow of images

HTML

<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>版本4 - innerHTML + 循環瀏覽</title>
</head>
<body>
  <div id="photoContainer"></div>
  <p id="status"></p>
  <button onclick="changePhoto(-1)">上一張</button>
  <button onclick="changePhoto(1)">下一張</button>

  <script>
    const photos = ["http://1.bp.blogspot.com/-xdHGOG59LCI/UjawN7V-deI/AAAAAAAABb8/v3dHRriJkjo/s1600/EUCL%E4%B8%8A%E5%8F%B0%E9%A0%98%E7%8D%8E01.jpg", 
                    "http://4.bp.blogspot.com/-UKB9Pburh8I/Ujawb7t3wGI/AAAAAAAABcE/2h3OMM1sb-0/s1600/Frocius+Android%E4%B8%8A%E5%8F%B0%E9%A0%98%E7%8D%8E01.jpg", 
                    "https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjUJYAY6cEyvTthq9s3Pz3RCayzcOM7UVffF8cmCk0XZBaAz7O6tLktSa7e1_f7Ni_ZxZaD8p4tLzqzhqnHo8rnsKuYvhPflJr2mAZeOSayg3sHjXCrrOtJ7cqPP6OdZAEJsHYJ5QWPTXw/s640/R0010396.JPG"];
    let index = 0;
    const container = document.getElementById("photoContainer");
    const statusEl = document.getElementById("status");

    function updateView() {
      container.innerHTML = '<img src="' + photos[index] + '" width="300">';
      statusEl.textContent = (index + 1) + " / " + photos.length;
    }

    function changePhoto(step) {
      index = (index + step + photos.length) % photos.length;
      updateView();
    }

    updateView();
  </script>
</body>
</html>