leader-tab/dist/index.mjs

An algorithm for selecting a leader from all the open tabs of a website.

// src/index.ts
var defaultParams = {
  channelName: "leader-election",
  heartbeatInterval: 50,
  deathTimeout: 500
};
function elector({ onLeaderElected, onLeaderDemoted } = {
  onLeaderElected: () => {
  },
  onLeaderDemoted: () => {
  }
}, {
  channelName = defaultParams.channelName,
  heartbeatInterval = defaultParams.heartbeatInterval,
  deathTimeout = defaultParams.deathTimeout
} = defaultParams) {
  const tabId = crypto.randomUUID();
  const channel = new BroadcastChannel(channelName);
  const knownTabs = /* @__PURE__ */ new Map();
  let isLeader = false;
  function heartbeat() {
    channel.postMessage({ type: "heartbeat", tabId });
    knownTabs.set(tabId, Date.now());
    electLeader();
  }
  function cleanup() {
    const now = Date.now();
    for (const [id, lastSeen] of knownTabs.entries()) {
      if (now - lastSeen > deathTimeout) {
        knownTabs.delete(id);
      }
    }
    electLeader();
  }
  function electLeader() {
    const sorted = [...knownTabs.keys()].sort();
    const newLeader = sorted[0];
    const wasLeader = isLeader;
    isLeader = newLeader === tabId;
    if (isLeader && !wasLeader) {
      onLeaderElected();
    } else if (!isLeader && wasLeader) {
      onLeaderDemoted();
    }
  }
  function handleMessage(event) {
    const msg = event.data;
    if (msg.type === "heartbeat") {
      knownTabs.set(msg.tabId, Date.now());
    } else if (msg.type === "goodbye") {
      knownTabs.delete(msg.tabId);
    }
  }
  channel.addEventListener("message", handleMessage);
  function sendGoodbye() {
    channel.postMessage({ type: "goodbye", tabId });
  }
  if (typeof window !== "undefined" && window.addEventListener) {
    window.addEventListener("beforeunload", sendGoodbye);
  }
  const heartbeatIntervalId = setInterval(heartbeat, heartbeatInterval);
  const cleanupIntervalId = setInterval(cleanup, heartbeatInterval);
  return Object.freeze({
    isLeader: () => isLeader,
    getTabId: () => tabId,
    destroy: () => {
      clearInterval(heartbeatIntervalId);
      clearInterval(cleanupIntervalId);
      channel.removeEventListener("message", handleMessage);
      if (typeof window !== "undefined" && window.removeEventListener) {
        window.removeEventListener("beforeunload", sendGoodbye);
      }
      sendGoodbye();
    }
  });
}
export {
  elector
};