Workers can be used to run code on multiple threads. Each instance of Worker is run on a separate thread, dedicated only to that worker.

Currently Deno supports only module type workers; thus it’s essential to pass the type: "module" option when creating a new worker.

Relative module specifiers are at the moment. You can instead use the URL contructor and import.meta.url to easily create a specifier for some nearby script.

Creating a new Worker instance is similar to a dynamic import; therefore Deno requires appropriate permission for this action.

For workers using local modules; --allow-read permission is required:

new Worker(new URL("worker.ts", import.meta.url).href, { type: "module" });

worker.ts

console.log("hello world");
self.close();

For workers using remote modules; permission is required:

main.ts

new Worker("https://example.com/worker.ts", { type: "module" });

worker.ts (at https://example.com/worker.ts)

self.close();

Using Deno in worker

To add the Deno namespace pass deno: true option when creating new worker:

main.js

const worker = new Worker(new URL("worker.js", import.meta.url).href, {
  type: "module",
  deno: true,
});

worker.js

  const { filename } = e.data;
  const text = await Deno.readTextFile(filename);
  console.log(text);
  self.close();
};

log.txt

$ deno run --allow-read --unstable main.js

When the Deno namespace is available in worker scope, the worker inherits its parent process’ permissions (the ones specified using --allow-* flags).