fix: Use duck typing to differentiate between a dedicated and a shared worker (#30)

Author: webJose

README.md

@@ -1,25 +1,16 @@
 # @wjfe/async-workers
 
-> Provides thread-safe and atomic synchronization objects, and wrappers to easily use web workers with async/await 
-> syntax.
+> Thread-safe, atomic synchronization objects and asynchronous worker wrappers for the browser and Node environments
 
 [Live Demo](https://wjsoftware.github.io/wjfe-async-workers)
 
-> [!CAUTION]
-> This NPM package is in its experimental phase.  Features may be incomplete or still requiring thorough testing.
+> **⚠️ Caution!**
+> This NPM package has had minimal testing under NodeJS + web-worker.
 
-## Introduction
+## Objectives
 
-Using web workers imply a call to `Worker.postMessge()` to signal the worker you want the work done, and then expect 
-some notification back via a listener in `Worker.onmessage` to at least know that the work completed, but usually to 
-get a result back in the form of data (the result of the work).  This is just the core, though.  You should also add 
-a listener to `Worker.onerror` just in case the worker has issues processing your request.  Otherwise you'll be waiting 
-forever for the notification, ignorant that an error has occurred and nothing will ever be returned.
-
-Oh, but this is just on the user interface side.  Then there's the matter of doing the web worker side.  No point in 
-continuing the explanation.  The point is made:  This is incredibly cumbersome.  Multi-threaded runtimes like .Net can 
-use `async/await` with threads and is far more convenient.  The whole point of this NPM package is to bring this 
-convenience to the web workers world.
+1. To provide friendly `async/await` syntax to the Node and web workers world.
+2. To provide thread-safe, atomic synchronization objects like the ones found in other runtimes like .Net
 
 ## Quickstart
 
@@ -30,7 +21,7 @@ to incoming messages.
 2. Export the tasks worker object.
 3. Create a new instance of `Worker` the way is recommended by your bundler, usually with the syntax 
 `new Worker("./myworker.js", impot.meta.url)`.  However, this forces you to write the worker in JavaScript, at least 
-for Vite-powered projects.
+in Vite-powered projects.
 4. Create a new instance of `AsyncWorker` (from this package) by passing the worker object and the tasks object from 
 the previous points.
 5. Start worker tasks by using the `AsyncWorker.enqueue` property.  The functions found in this object return an object 
@@ -83,11 +74,13 @@ self.onmessage = workerListener(myWorker);
 
 This is a 3-step worker.  The worker simply waits to be informed which step to run from the user interface thread.
 
+> ℹ️ Worker tasks may take zero arguments.  This is perfectly valid.
+
 ### The Async Worker in the UI Thread
 
 This is what needs to be done in order to obtain an object that commands the worker:
 
-> [!IMPORTANT]
+> **⚡ Important**
 > This example is using TypeScript and the following assumes a Vite-powered project.  We are deviating from the 
 > recommended way of obtaining a worker because the recommended way requires the worker to be written in JavaScript 
 > while in serve mode (`npm run dev`).
@@ -120,6 +113,17 @@ Yes!  The above is valid:  You may queue up as many tasks as you wish without ha
 previous ones, even if the worker is asynchronous (uses `async/await`).  The worker controller will keep perfect record 
 of the order in which the tasks must be run.
 
+This table shows through examples how various call signatures change from from worker to enqueue object:
+
+| Worker Function | Enqueue Function |
+| - | - |
+| `init(config: Configuration): void;` | `init(payload: Configuration, options?: QueueingOptions): WorkItem<void>;` |
+| `sort(array: MyData[]): MyData[];` | `sort(payload: MyData[], options?: QueueingOptions): WorkItem<MyData[]>;` |
+| `shutdown(): void;` | `shutdown(payload: void, options?: QueueingOptions): WorkItem<void>;` |
+| `primesBetween(payload: { a: number; b: number; }): number[];` | `primesBetween(payload: { a: number; b: number }): WorkItem<number[]>;` |
+
+Task functions can only take zero or 1 parameter, so if more than one piece of data is needed as payload, pass an object with all the data, as the last example does.
+
 ## Shared Workers
 
 Shared workers are also supported through the same `AsyncWorker` class.  Note, however, the following key differences:
@@ -139,6 +143,9 @@ self.onconnect = (ev) => {
 
 ## Bi-Directional Communication
 
+> **🕓 TL;DR**
+> It's OK for workers to transmit intermediate results like progress reports and partial results.  It is not recommended for the main thread to have to send data to a paused task.  Promises in work item objects resolve once the `QueueingOptions.processMessage()` function returns `true`.
+
 The default functionality is fine for many cases:  A worker task is started, the user interface waits for its 
 completion and when the task finishes, the work item's `promise` property spits out the resultant object when awaited.
 
@@ -214,7 +221,7 @@ const defaultRunningTotalWorkItem = myWorkerController.enqueue.calculateRunningT
 });
 ```
 
-This is it.  Bi-directional communcation is fully set up.
+This is it.  Bi-directional communication is fully set up.
 
 ### How About Sending Something Back?
 
@@ -246,6 +253,31 @@ export const myWorker = {
 Inside `processMessage`, do `myWorkerController.enqueue.supplyMissingOrUpdatedDataWhileInTheAir(theData, { outOfOrder: true })`
 and hope for the best.
 
+## Worker Task Cancellation
+
+To fully understand, read [this topic](#cancellationsource) in the section about synchronization objects (coming up next), and also [this other topic about WorkItem class](#the-workitem-class).
+
+To use a cancellation token, specify the `cancellable` option when the task is enqueued:
+
+```typescript
+const workItem = myWorkerController.enqueue.doSomething(somePayload, { cancellable: true });
+...
+// If so needed, cancel at some point.
+workItem.cancel();
+...
+// At any point where the promise is awaited, an error will be thrown.
+try {
+    const result = await workItem.promise;
+}
+catch (err: unknown) {
+    if (err instanceof CancelledMessage) {
+        // The task was cancelled.
+    }
+}
+```
+
+To learn about the implementation in the worker side, keep reading.
+
 ## Synchronization Objects
 
 This package provides synchronization objects that use `Atomics` to cross the thread boundary safely.
@@ -286,7 +318,7 @@ is already simplified.  Taking one line from the quickstart example:
 const defaultRunningTotalWorkItem = myWorkerController.enqueue.calculateRunningTotal(undefined, { cancellable: true });
 ```
 
-By adding the `cancellable` option, a cancellation token will be avilable to `calculateRunningTotal` in its third 
+By adding the `cancellable` option, a cancellation token will be available to `calculateRunningTotal` in its third 
 parameter, as seen in the previous section.
 
 Whenever cancellation is desired, simply call the work item's `cancel()` method.  For more information about this 

src/workers/AsyncWorker.ts

@@ -6,6 +6,23 @@ import { InternalWorker } from "./InternalWorker.js";
 import { WorkItem } from "./WorkItem.js";
 import { WorkItemInternal } from "./WorkItemInternal.js";
 
+/**
+ * Determines if a worker-like object is a SharedWorker using duck typing.
+ * @param worker The worker object to test
+ * @returns true if the worker appears to be a SharedWorker, false otherwise
+ */
+function isSharedWorker(worker: any): worker is SharedWorker {
+    // SharedWorker has a 'port' property (MessagePort) with the required methods
+    return worker && 
+           typeof worker === 'object' &&
+           'port' in worker && 
+           worker.port && 
+           typeof worker.port === 'object' &&
+           typeof worker.port.postMessage === 'function' && 
+           typeof worker.port.addEventListener === 'function' &&
+           typeof worker.port.removeEventListener === 'function';
+}
+
 export type EnqueueFn<Fn extends ((...args: any[]) => any) = (() => any)> =
     (payload: Fn extends () => any ? void : Parameters<Fn>[0], options?: QueueingOptions) => WorkItem<ReturnType<Fn>>;
 
@@ -55,7 +72,7 @@ export class AsyncWorker<Tasks extends Record<string, (...args: any[]) => any>>
     #taskRunning;
     #enqueue;
     constructor(worker: Worker | SharedWorker, tasks: Tasks) {
-        this.#iWorker = Object.getPrototypeOf(worker).name === 'Worker' ? new InternalWorker(worker as Worker) : new InternalSharedWorker(worker as SharedWorker);
+        this.#iWorker = isSharedWorker(worker) ? new InternalSharedWorker(worker) : new InternalWorker(worker as Worker);
         this.#queue = new Queue<WorkItemInternal>();
         this.#taskRunning = false;
         this.#enqueue = Object.keys(tasks).reduce((prev, curr) => {