Macil / worker-message-queuer

Deno library to prevent worker threads from missing messages

worker-message-queuer

This is a Deno module for queuing messages sent to a worker thread while top-level await is used in order to prevent missed messages.

In Javascript, a Web Worker module is expected to immediately synchronously attach a message event listener to itself (through self.onmessage = ... or self.addEventListener("message", ...)), or else messages sent to it before the message event listener is attached will be lost. This is a problem when using top-level await before attaching the message event listener because the worker may receive messages before the top-level await is finished. This situation easily arises when a worker module imports dependencies that use top-level await internally.

This module solves issues like Worker's postMessage not working.

Usage

In a web worker, use the addMessageEventListener function from this module instead of self.onmessage = ... to attach your message event listener and process all queued events:

import { addMessageEventListener } from "https://deno.land/x/worker_message_queuer@v1.0.1/mod.ts";
import { exampleFunction } from "example/module-using-top-level-await";

addMessageEventListener((event) => {
  console.log("Received message:", event.data);
});

As long as this module is statically imported in the worker module, it does not matter whether it is imported before or after other imports containing top-level await.