fix: align DedicatedWorkerGlobalScope event handlers to spec (#11353)

6 files changed, 81 insertions, 32 deletions

diff --git a/cli/tests/integration/run_tests.rs b/cli/tests/integration/run_tests.rs
index d2997d747..2e2b0400c 100644
--- a/cli/tests/integration/run_tests.rs
+++ b/cli/tests/integration/run_tests.rs
@@ -1155,6 +1155,11 @@ itest!(error_import_map_unable_to_load {
   exit_code: 1,
 });
 
+itest!(worker_event_handler_test {
+  args: "run --quiet --reload --allow-read worker_event_handler_test.js",
+  output: "worker_event_handler_test.js.out",
+});
+
 #[test]
 fn no_validate_asm() {
   let output = util::deno_cmd()
diff --git a/cli/tests/worker_event_handler_test.js b/cli/tests/worker_event_handler_test.js
new file mode 100644
index 000000000..e0ce3d9f8
--- /dev/null
+++ b/cli/tests/worker_event_handler_test.js
@@ -0,0 +1,5 @@
+const w = new Worker(
+  new URL("./workers/worker_event_handlers.js", import.meta.url).href,
+  { type: "module" },
+);
+w.postMessage({});
diff --git a/cli/tests/worker_event_handler_test.js.out b/cli/tests/worker_event_handler_test.js.out
new file mode 100644
index 000000000..5556633b1
--- /dev/null
+++ b/cli/tests/worker_event_handler_test.js.out
@@ -0,0 +1,11 @@
+Target from self.onmessage: [object DedicatedWorkerGlobalScope]
+Target from message event listener: [object DedicatedWorkerGlobalScope]
+Arguments from self.onerror: [
+  "Some error message",
+  "",
+  0,
+  0,
+  Error: Some error message
+    at [WILDCARD]
+]
+Is event canceled?: true
diff --git a/cli/tests/workers/worker_event_handlers.js b/cli/tests/workers/worker_event_handlers.js
new file mode 100644
index 000000000..c8976f79e
--- /dev/null
+++ b/cli/tests/workers/worker_event_handlers.js
@@ -0,0 +1,23 @@
+self.onmessage = (evt) => {
+  console.log("Target from self.onmessage:", String(evt.target));
+};
+
+self.addEventListener("message", (evt) => {
+  console.log("Target from message event listener:", String(evt.target));
+
+  // Throw an error here so the global's error event will fire.
+  throw new Error("Some error message");
+});
+
+self.onerror = (...args) => {
+  console.log("Arguments from self.onerror:", args);
+  return true;
+};
+
+self.addEventListener("error", (evt) => {
+  // Returning true from self.onerror means that subsequent event listeners
+  // should see the event as canceled.
+  console.log("Is event canceled?:", evt.defaultPrevented);
+
+  self.close();
+});
diff --git a/runtime/js/01_web_util.js b/runtime/js/01_web_util.js
index 4a9825fa1..9b51021f9 100644
--- a/runtime/js/01_web_util.js
+++ b/runtime/js/01_web_util.js
@@ -27,17 +27,41 @@
   }
 
   const handlerSymbol = Symbol("eventHandlers");
-  function makeWrappedHandler(handler) {
+  function makeWrappedHandler(handler, isSpecialErrorEventHandler) {
     function wrappedHandler(...args) {
       if (typeof wrappedHandler.handler !== "function") {
         return;
       }
+      if (isSpecialErrorEventHandler) {
+        const evt = args[0];
+        if (evt instanceof ErrorEvent && evt.type === "error") {
+          const ret = FunctionPrototypeCall(
+            wrappedHandler.handler,
+            this,
+            evt.message,
+            evt.filename,
+            evt.lineno,
+            evt.colno,
+            evt.error,
+          );
+          if (ret === true) {
+            evt.preventDefault();
+          }
+          return;
+        }
+      }
+
       return FunctionPrototypeCall(wrappedHandler.handler, this, ...args);
     }
     wrappedHandler.handler = handler;
     return wrappedHandler;
   }
-  function defineEventHandler(emitter, name, defaultValue = undefined) {
+  function defineEventHandler(
+    emitter,
+    name,
+    defaultValue = undefined,
+    isSpecialErrorEventHandler = false,
+  ) {
     // HTML specification section 8.1.5.1
     ObjectDefineProperty(emitter, `on${name}`, {
       get() {
@@ -56,7 +80,10 @@
         if (handlerWrapper) {
           handlerWrapper.handler = value;
         } else {
-          handlerWrapper = makeWrappedHandler(value);
+          handlerWrapper = makeWrappedHandler(
+            value,
+            isSpecialErrorEventHandler,
+          );
           this.addEventListener(name, handlerWrapper);
         }
         MapPrototypeSet(this[handlerSymbol], name, handlerWrapper);
diff --git a/runtime/js/99_main.js b/runtime/js/99_main.js
index b473acdef..71480e5a0 100644
--- a/runtime/js/99_main.js
+++ b/runtime/js/99_main.js
@@ -88,11 +88,6 @@ delete Object.prototype.__proto__;
     core.opSync("op_worker_close");
   }
 
-  // TODO(bartlomieju): remove these functions
-  // Stuff for workers
-  const onmessage = () => {};
-  const onerror = () => {};
-
   function postMessage(message, transferOrOptions = {}) {
     const prefix =
       "Failed to execute 'postMessage' on 'DedicatedWorkerGlobalScope'";
@@ -144,39 +139,19 @@ delete Object.prototype.__proto__;
       });
 
       try {
-        if (globalThis.onmessage) {
-          await globalThis.onmessage(msgEvent);
-        }
         globalDispatchEvent(msgEvent);
       } catch (e) {
-        let handled = false;
-
         const errorEvent = new ErrorEvent("error", {
           cancelable: true,
           message: e.message,
           lineno: e.lineNumber ? e.lineNumber + 1 : undefined,
           colno: e.columnNumber ? e.columnNumber + 1 : undefined,
           filename: e.fileName,
-          error: null,
+          error: e,
         });
 
-        if (globalThis["onerror"]) {
-          const ret = globalThis.onerror(
-            e.message,
-            e.fileName,
-            e.lineNumber,
-            e.columnNumber,
-            e,
-          );
-          handled = ret === true;
-        }
-
         globalDispatchEvent(errorEvent);
-        if (errorEvent.defaultPrevented) {
-          handled = true;
-        }
-
-        if (!handled) {
+        if (!errorEvent.defaultPrevented) {
           core.opSync(
             "op_worker_unhandled_error",
             e.message,
@@ -465,8 +440,8 @@ delete Object.prototype.__proto__;
       get: () => workerNavigator,
     },
     self: util.readOnly(globalThis),
-    onmessage: util.writable(onmessage),
-    onerror: util.writable(onerror),
+    onmessage: util.writable(null),
+    onerror: util.writable(null),
     // TODO(bartlomieju): should be readonly?
     close: util.nonEnumerable(workerClose),
     postMessage: util.writable(postMessage),
@@ -585,6 +560,9 @@ delete Object.prototype.__proto__;
 
     eventTarget.setEventTargetData(globalThis);
 
+    defineEventHandler(self, "message", null);
+    defineEventHandler(self, "error", null, true);
+
     runtimeStart(
       runtimeOptions,
       internalName ?? name,