查看，设置，设备的 竖屏-横屏模式 screen.orientation

<body>
  <div id="doc"></div>
  <div id="model"></div>
  <script>
    let a = 0;
  if ('orientation' in screen) {
    document.getElementById('doc').textContent = `屏幕旋转了${a}次.`;
    document.getElementById('model').textContent = `当前为${screen.orientation.type}模式！`;

    screen.orientation.addEventListener('change', function () {// 监听屏幕的旋转
      a++;
      document.getElementById('doc').textContent = `屏幕旋转了${a}次.`;
      if (screen.orientation.type.startsWith('landscape')) {
        document.getElementById('model').textContent = `当前为横屏模式！`;
      } else {
        document.getElementById('model').textContent = `当前为纵向模式！`;
      }
    });
  }
  </script>
</body>

screen.orientation.lock 开发者主动切换 landscape 和 portrait 模式

对应的 screen.orientation.unlock();

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<html class="no-js">
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<html lang="zh-cmn-Hans">

<head>
  <meta charset="utf-8">
  <title>video 全屏体验</title>
  <link rel="shortcut icon" type="image/ico" href="" />
  <meta name="viewport" content="width=device-width, initial-scale=1.0" />
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  <meta name="renderer" content="webkit" />
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  <!--禁止浏览器从本地计算机的缓存中访问页面内容-->
  <meta http-equiv="Window-target" content="_top" />
  <!--强制页面在当前窗口以独立页面显示-->
  <meta http-equiv="content-Type" content="text/html;charset=utf-8" />
  <!--显示字符集的设定-->
  <meta http-equiv="Content-Language" content="zh-cn" />
  <!--显示语言的设定-->
  <meta http-equiv="imagetoolbar" content="false" />
  <!--指定是否显示图片工具栏，false不显示,true显示-->
  <link rel="icon" sizes="192x192" href="https://pic.cnblogs.com/avatar/1053296/20171128213246.png" />
  <link rel="apple-touch-icon" href="https://pic.cnblogs.com/avatar/1053296/20171128213246.png" />
  <meta name="msapplication-square310x310logo" content="https://pic.cnblogs.com/avatar/1053296/20171128213246.png" />
  <meta name="theme-color" content="#ff4081" />
  <meta name="apple-mobile-web-app-status-bar-style" content="black-translucent" />
  <!-- Chrome, Firefox OS and Opera -->
  <link rel="apple-touch-startup-image" href="https://pic.cnblogs.com/avatar/1053296/20171128213246.png" />
  <style>
    .full-img {
      max-width: 100%;
    }
  </style>
</head>

<body>
  <!--[if lt IE 8]>  <h3>请升级你的浏览器，或更换主浏览器！！!</h3>  <![endif]-->
  <img class="full-img" src="http://per.kelantu.com/photos/1515232896-FnIf9c57Hf1-l7DUdBwlXdN1bcLv-orij0?e=3153600000&token=CT86R8zZYVXDyHWEWFoMX4pz0ksOzxtKCaC80si4:HcaTgLGmJ6IbOt_d9ZGOQIqtv6g="
    alt="">
  <div class="doc"></div>
  <script>
    let img = document.querySelector('.full-img');
    img.addEventListener('click', function (e) {
      if (document.requestFullscreen) {
        // 存在全屏 元素就退出全屏
        document.exitFullscreen();
      } else {
        requestFullscreenImage();
        lockScreenInLandscape();
      }
    }, false);

    function requestFullscreenImage() {
      if (img.requestFullscreen) {
        img.requestFullscreen();
      } else {
        img.webkitRequestFullscreen();
      }
    }

    function lockScreenInLandscape() {
      if (!('orientation' in screen)) {
        return;
      }

      // 判断当前 设备是 竖屏还是 横屏
      // portrait 竖屏
      // landscape 横屏
      if (matchMedia('(orientation: portrait) and (max-device-width: 768px)').matches) {
        // 竖屏就变 横屏
        screen.orientation.lock('landscape').then(function () {
          setTimeout(()=>{
            screen.orientation.unlock();
            // document.exitFullscreen();
            document.webkitExitFullscreen()
          }, 2000);
        });
      }
    }
  </script>
</body>

</html>