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Remote Worker

Leightweight (~0.3kb) Worker patch to allow loading scripts from remote URLs (cross-origin).

Motivation

Allows to host Web Worker scripts on CDN servers without the following cors exceptions:

  • Uncaught DOMException: Failed to construct 'Worker': Script at 'https://cdn.jsdelivr.net/npm/console-log-hello-world' cannot be accessed from origin 'http://localhost:8080'.
  • Uncaught (in promise) DOMException: Failed to execute 'importScripts' on 'WorkerGlobalScope': The script at 'https://cdn.jsdelivr.net/npm/console-log-hello-world' failed to load.

Installation

npm install --save-dev remote-web-worker

Usage

Apply Patch

import 'remote-web-worker';

Initialize a Worker just like you would normally do:

const worker = new Worker(
  'https://cdn.jsdelivr.net/npm/console-log-hello-world',
  { type: 'classic' }
);

How it works

According to spec the Worker constructor accepts only local URLs, not remote URLs: https://developer.mozilla.org/en-US/docs/Web/API/Worker/Worker

As a workaround this patched Worker will use importScripts to load the remote script. https://developer.mozilla.org/en-US/docs/Web/API/WorkerGlobalScope/importScripts

Compatibility

  • Chrome 4+
  • Firefox 4+
  • Safari 4+

Limitations

  • Only supports type="classic" workers (no import or export)

Security

The remote script is loaded via importScripts which is not subject to CORS.
However, the script is loaded in a separate context and cannot access the main thread or the DOM. The remote script runs in the current sites origin and therefore will not be able to access Cookies or Local Storage of the remote server.

License

MIT