Use addEventListener instead of onmessage in WebWorkerPostMessage…

…Stream (#83)

* Use addEventListener instead of onmessage in WebWorkerPostMessageStream constructor

The use of addEventListener allows proper handling of multiple event listeners. onmesssage also does not work with LavaMoat.

* Remove test for throwing error when not run in a WebWorker

This test is now unnecessary.

* Refactor WebWorkerPostMessageStream test using mocked self

The test was trying to use globalThis.self variable, but it is not always defined in the test
environment. To fix the issue, the variable can be created as a mock object before
each test, and restored to the original value after it finishes.

src/WebWorker/WebWorker.test.ts

@@ -84,26 +84,26 @@ describe('WebWorker Streams', () => {
       );
     });
 
-    it('throws if not run in a WebWorker (self not an instance of WorkerGlobalScope)', () => {
-      (globalThis as any).self = originalSelf;
-      expect(() => new WebWorkerPostMessageStream()).toThrow(
-        'WorkerGlobalScope not found. This class should only be instantiated in a WebWorker.',
-      );
-    });
-
     it('can be destroyed', () => {
+      (globalThis as any).self = originalSelf;
       const stream = new WebWorkerPostMessageStream();
       expect(stream.destroy()).toBeUndefined();
     });
 
     it('forwards valid messages', () => {
+      (globalThis as any).self = originalSelf;
+      const addEventListenerSpy = jest.spyOn(globalThis, 'addEventListener');
       const stream = new WebWorkerPostMessageStream();
+
       const onDataSpy = jest
         .spyOn(stream, '_onData' as any)
         .mockImplementation();
 
+      expect(addEventListenerSpy).toHaveBeenCalledTimes(1);
+      const listener = addEventListenerSpy.mock.calls[0][1] as EventListener;
+
       // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
-      self.onmessage!(
+      listener(
         new MessageEvent('foo', {
           data: { data: 'bar', target: DEDICATED_WORKER_NAME },
         }),
@@ -114,11 +114,17 @@ describe('WebWorker Streams', () => {
     });
 
     it('ignores invalid messages', () => {
+      (globalThis as any).self = originalSelf;
+      const addEventListenerSpy = jest.spyOn(globalThis, 'addEventListener');
       const stream = new WebWorkerPostMessageStream();
+
       const onDataSpy = jest
         .spyOn(stream, '_onData' as any)
         .mockImplementation();
 
+      expect(addEventListenerSpy).toHaveBeenCalledTimes(2);
+      const listener = addEventListenerSpy.mock.calls[0][1] as EventListener;
+
       (
         [
           { data: 'bar' },
@@ -127,7 +133,7 @@ describe('WebWorker Streams', () => {
         ] as const
       ).forEach((invalidMessage) => {
         // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
-        self.onmessage!(new MessageEvent<unknown>('foo', invalidMessage));
+        listener(new MessageEvent<unknown>('foo', invalidMessage));
 
         expect(onDataSpy).not.toHaveBeenCalled();
       });

src/WebWorker/WebWorkerPostMessageStream.ts

@@ -22,9 +22,7 @@ export class WebWorkerPostMessageStream extends BasePostMessageStream {
     if (
       typeof self === 'undefined' ||
       // @ts-expect-error: No types for WorkerGlobalScope
-      typeof WorkerGlobalScope === 'undefined' ||
-      // @ts-expect-error: No types for WorkerGlobalScope
-      !(self instanceof WorkerGlobalScope)
+      typeof WorkerGlobalScope === 'undefined'
     ) {
       throw new Error(
         'WorkerGlobalScope not found. This class should only be instantiated in a WebWorker.',
@@ -34,7 +32,7 @@ export class WebWorkerPostMessageStream extends BasePostMessageStream {
     super();
 
     this._name = DEDICATED_WORKER_NAME;
-    self.onmessage = this._onMessage.bind(this) as any;
+    self.addEventListener('message', this._onMessage.bind(this) as any);
 
     this._handshake();
   }