擴充功能情境之間的訊息傳遞

// 錯誤：監聽器在 await 落定前就回傳了，通道因此關閉。
chrome.runtime.onMessage.addListener((message, sender, sendResponse) => {
  fetchSettings().then((settings) => sendResponse({ ok: true, settings }));
});

// 正確：回傳 true 會讓通道保持開啟，直到 sendResponse 執行。
chrome.runtime.onMessage.addListener((message, sender, sendResponse) => {
  fetchSettings().then((settings) => sendResponse({ ok: true, settings }));
  return true;
});

type Message =
  | { type: "settings:get" }
  | { type: "settings:set"; payload: { theme: "light" | "dark" } };

chrome.runtime.onMessage.addListener((message: Message, sender, sendResponse) => {
  if (!message || typeof message.type !== "string") {
    sendResponse({ ok: false, error: "invalid_message" });
    return;
  }

  if (message.type === "settings:get") {
    getSettings().then((settings) => sendResponse({ ok: true, settings }));
    return true;
  }

  sendResponse({ ok: false, error: "unknown_message" });
});

// Content script。
const port = chrome.runtime.connect({ name: "highlights" });
port.postMessage({ type: "subscribe" });
port.onMessage.addListener((update) => render(update));

// Service worker。
chrome.runtime.onConnect.addListener((port) => {
  if (port.name !== "highlights") return;
  port.onMessage.addListener((message) => port.postMessage({ ok: true }));
  port.onDisconnect.addListener(() => stopWatching(port));
});