Bring the Worker polyfill up to the Dedicated Worker spec

.github/workflows/ci.yml

@@ -0,0 +1,27 @@
+name: CI
+
+on:
+  push:
+  pull_request:
+
+jobs:
+  node_tests:
+    name: Node tests
+    runs-on: ubuntu-24.04
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Setup Node
+        uses: actions/setup-node@v4
+        with:
+          node-version: "20"
+
+      - name: Install dependencies
+        run: npm ci
+
+      - name: Build
+        run: npm run build
+
+      - name: Test
+        run: npm run test:run

.gitignore

@@ -4,4 +4,3 @@
 
 lib/
 node_modules/
-package-lock.json

LICENSE

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+Copyright (c) 2021 Pau Marfany <p.marfany_96@hotmail.com>
+Copyright (c) 2026 Xe Iaso <me@xeiaso.net>
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in
+all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+THE SOFTWARE.

README.md

@@ -1,46 +1,92 @@
 # worker-polyfill
 
-A simple script that emulates web worker threads in non compatible browsers.
-The code will still be slow (single threaded) but you can keep you code consistent.
+A small polyfill that emulates the Dedicated [Web Worker API](https://developer.mozilla.org/en-US/docs/Web/API/Worker)
+in browsers that don't support it (Internet Explorer and other old browsers).
+The code is still single-threaded, but it lets you keep one consistent code
+path. Messages are structured-cloned and delivered asynchronously, matching
+the spec's observable behaviour.
 
-Usage:
-```js
-// You must check for compatibility before loading the polyfill
-if ( !Worker ) { require('worker-loader'); }
+## Install
+
+The polyfill installs itself as the global `Worker` **only if the browser has
+no native implementation**, so it is safe to include unconditionally:
+
+```html
+<script src="worker-polyfill.js"></script>
 ```
 
-Workers can be loaded and used as usual:
+## Usage
+
+Workers are created and used as usual:
+
 ```js
-var worker = new Worker("your_script.js");  
+var worker = new Worker("your_script.js");
 
-worker.onmessage = function(event) {  
-    alert("Got: " + event.data);  
-};  
+worker.onmessage = function (event) {
+  alert("Got: " + event.data);
+};
 
-worker.onerror = function(error) {  
-    alert("Worker error: " + error);  
+worker.onerror = function (event) {
+  alert("Worker error: " + event.message);
 };
 
-worker.postMessage("Hello World"); 
+worker.postMessage("Hello World");
 ```
 
-'addEventListener' methods are also supported:
+`addEventListener` is supported with full multi-listener semantics:
 
 ```js
-var worker = new Worker("your_script.js");
-
-worker.addEventListener("message", function(event) {  
-    alert("Got: " + event.data);  
+worker.addEventListener("message", function (event) {
+  alert("Got: " + event.data);
 });
-
-worker.addEventListener("error", function(error) {  
-    alert("Worker error: " + error);  
+worker.addEventListener("error", function (event) {
+  alert("Worker error: " + event.message);
 });
+```
 
-worker.postMessage("Hello World");
+Inside the worker script, the usual idioms work because the script runs in its
+own scope:
+
+```js
+// your_script.js
+self.onmessage = function (event) {
+  self.postMessage("echo: " + event.data);
+};
+// importScripts() is supported and runs synchronously
+// close() stops the worker
 ```
 
-- For more info on worker threads see
-https://developer.mozilla.org/En/Using_web_workers
+## Supported
+
+`postMessage` (structured-cloned, ordered), `terminate`, `close`,
+`addEventListener`/`removeEventListener`/`dispatchEvent`, `message`/`error`
+events, `importScripts` (synchronous), `self`/`name`.
+
+## Not supported
+
+Module workers (`type: "module"`), transferable objects, `blob:`/`data:` URLs,
+`credentials`, and real OS-thread parallelism. Pass plain, cloneable data.
+
+## Limitations
+
+`importScripts()` is synchronous and executes imported scripts immediately,
+but top-level `var`/`function` declarations in an imported script are NOT
+visible to the main worker script (or vice versa). Use `self.X = ...`
+assignments (which land on the worker scope) to share values across scripts
+loaded via `importScripts()`.
+
+The bare identifier `arguments` (and the internal parameter names
+`__worker_scope__` and `__worker_src__`) are shadowed inside top-level
+worker code due to the Function constructor wrapper—avoid using `arguments`
+as an identifier in worker scripts.
+
+## Development
+
+```bash
+npm install
+npm test        # vitest + jsdom conformance suite
+npm run build   # webpack UMD bundle into lib/
+```
 
+- For more on workers see https://developer.mozilla.org/en-US/docs/Web/API/Web_Workers_API
 - Originally exported from Google Code (https://code.google.com/p/ie-web-worker/).