Document：fullscreenchange 事件

addEventListener("fullscreenchange", (event) => {});

onfullscreenchange = (event) => {};

<h1>fullscreenchange 事件示例</h1>
<div id="fullscreen-div">
  <button id="toggle-fullscreen">切换全屏模式</button>
  <pre id="logger"></pre>
</div>

* {
  box-sizing: border-box;
}

#fullscreen-div {
  height: 150px;
  padding: 1rem;
  background-color: pink;
}

#logger {
  height: 80px;
  padding: 0 0.5rem;
  background-color: white;
  overflow: scroll;
}

const logger = document.querySelector("#logger");
const fullScreenElement = document.querySelector("#fullscreen-div");

function log(message) {
  logger.textContent = `${logger.textContent}\n${message}`;
}

function fullscreenchangeHandler(event) {
  // 如果有元素处于全屏模式，则 document.fullscreenElement 将指向该元素。如果没有元素处于全屏模式，则该属性的值为 null。
  if (document.fullscreenElement) {
    log(`元素：${document.fullscreenElement.id} 进入全屏模式。`);
  } else {
    log("退出全屏模式。");
  }
}

document.addEventListener("fullscreenchange", fullscreenchangeHandler);

// 在切换按钮被点击时，将会进入或退出全屏模式
document.getElementById("toggle-fullscreen").addEventListener("click", () => {
  if (document.fullscreenElement) {
    // exitFullscreen 方法只能在 Document 对象上使用。
    document.exitFullscreen();
  } else {
    fullScreenElement.requestFullscreen();
  }
});