{
  "addonid": "hello.world",
  "title": "你好世界",
  "version": "0.1.0",
  "author": "我",
  "marginnote_version_min": "4.5.0",
  "immersiveOnly": true,
  "panel": "index.html"
}

<!DOCTYPE html>
<html>

<body>
  <button onclick="ask()">现在开着哪个学习集？</button>
  <div id="out"></div>

  <script>
    async function ask() {
      var out = document.getElementById("out");
      try {
        var r = await mn.api("/ui-state");
        var t = r.state.topicid;
        out.textContent = t
          ? "当前学习集 id：" + t
          : "当前未打开学习集";
      } catch (e) {
        out.textContent = "出错了：" + e;
      }
    }
  </script>
</body>

</html>