index.js

let currentTimeoutId = undefined;
let isEnabled = false;
let controller = undefined;
let messagePorts = new Set();

exports.loadPackage = async function (
  gridController,
  persistedData
) {
  controller = gridController;
  isEnabled = true;
  runLoop();
};

exports.unloadPackage = async function () {
  controller = undefined;
  messagePorts.forEach((port) => port.close());
  messagePorts.clear();
  cancelLoop();
};

exports.addMessagePort = async function (port) {
  port.on("message", (e) => {
    onMessage(port, e.data);
  });

  messagePorts.add(port);
  port.on("close", () => {
    messagePorts.delete(port);
  });
  port.start();
};

async function onMessage(port, data) {
  if (data.type === "request-echo") {
    port.postMessage({
      type: "echo",
      message: "Echo message",
    });
  }
}

async function runLoop() {
  if (!isEnabled) return;

  messagePorts.forEach((port) =>
    port.postMessage({
      type: "echo",
      message: "Loop message",
    })
  );
  currentTimeoutId = setTimeout(runLoop, 2000);
}

function cancelLoop() {
  isEnabled = false;
  clearTimeout(currentTimeoutId);
}