feat(ext/web): Add error events for event listener and timer errors (#14159)

- feat: Add handleable error event for even listener errors
- feat: Add handleable error event for setTimeout()/setInterval() errors
- feat: Add Deno.core.destructureError()
- feat: Add Deno.core.terminate()
- fix: Don't throw listener errors from dispatchEvent()
- fix: Use biased mode when selecting between mod_evaluate() and
  run_event_loop() results

.github/workflows/ci.yml

@@ -236,7 +236,7 @@ jobs:
             ~/.cargo/registry/index
             ~/.cargo/registry/cache
             ~/.cargo/git/db
-          key: 5-cargo-home-${{ matrix.os }}-${{ hashFiles('Cargo.lock') }}
+          key: 7-cargo-home-${{ matrix.os }}-${{ hashFiles('Cargo.lock') }}
 
       # In main branch, always creates fresh cache
       - name: Cache build output (main)
@@ -252,7 +252,7 @@ jobs:
             !./target/*/*.zip
             !./target/*/*.tar.gz
           key: |
-            5-cargo-target-${{ matrix.os }}-${{ matrix.profile }}-${{ github.sha }}
+            7-cargo-target-${{ matrix.os }}-${{ matrix.profile }}-${{ github.sha }}
 
       # Restore cache from the latest 'main' branch build.
       - name: Cache build output (PR)
@@ -268,7 +268,7 @@ jobs:
             !./target/*/*.tar.gz
           key: never_saved
           restore-keys: |
-            5-cargo-target-${{ matrix.os }}-${{ matrix.profile }}-
+            7-cargo-target-${{ matrix.os }}-${{ matrix.profile }}-
 
       # Don't save cache after building PRs or branches other than 'main'.
       - name: Skip save cache (PR)

cli/dts/lib.deno.window.d.ts

@@ -7,10 +7,15 @@
 /// <reference lib="deno.webstorage" />
 /// <reference lib="esnext" />
 
+interface WindowEventMap {
+  "error": ErrorEvent;
+}
+
 declare class Window extends EventTarget {
   new(): Window;
   readonly window: Window & typeof globalThis;
   readonly self: Window & typeof globalThis;
+  onerror: ((this: Window, ev: ErrorEvent) => any) | null;
   onload: ((this: Window, ev: Event) => any) | null;
   onunload: ((this: Window, ev: Event) => any) | null;
   close: () => void;
@@ -25,10 +30,38 @@ declare class Window extends EventTarget {
   location: Location;
   localStorage: Storage;
   sessionStorage: Storage;
+
+  addEventListener<K extends keyof WindowEventMap>(
+    type: K,
+    listener: (
+      this: Window,
+      ev: WindowEventMap[K],
+    ) => any,
+    options?: boolean | AddEventListenerOptions,
+  ): void;
+  addEventListener(
+    type: string,
+    listener: EventListenerOrEventListenerObject,
+    options?: boolean | AddEventListenerOptions,
+  ): void;
+  removeEventListener<K extends keyof WindowEventMap>(
+    type: K,
+    listener: (
+      this: Window,
+      ev: WindowEventMap[K],
+    ) => any,
+    options?: boolean | EventListenerOptions,
+  ): void;
+  removeEventListener(
+    type: string,
+    listener: EventListenerOrEventListenerObject,
+    options?: boolean | EventListenerOptions,
+  ): void;
 }
 
 declare var window: Window & typeof globalThis;
 declare var self: Window & typeof globalThis;
+declare var onerror: ((this: Window, ev: ErrorEvent) => any) | null;
 declare var onload: ((this: Window, ev: Event) => any) | null;
 declare var onunload: ((this: Window, ev: Event) => any) | null;
 declare var localStorage: Storage;
@@ -77,10 +110,17 @@ declare function prompt(message?: string, defaultValue?: string): string | null;
  * dispatchEvent(new Event('unload'));
  * ```
  */
+declare function addEventListener<
+  K extends keyof WindowEventMap,
+>(
+  type: K,
+  listener: (this: Window, ev: WindowEventMap[K]) => any,
+  options?: boolean | AddEventListenerOptions,
+): void;
 declare function addEventListener(
   type: string,
-  callback: EventListenerOrEventListenerObject | null,
-  options?: boolean | AddEventListenerOptions | undefined,
+  listener: EventListenerOrEventListenerObject,
+  options?: boolean | AddEventListenerOptions,
 ): void;
 
 /** Remove a previously registered event listener from the global scope
@@ -91,10 +131,17 @@ declare function addEventListener(
  * removeEventListener('load', listener);
  * ```
  */
+declare function removeEventListener<
+  K extends keyof WindowEventMap,
+>(
+  type: K,
+  listener: (this: Window, ev: WindowEventMap[K]) => any,
+  options?: boolean | EventListenerOptions,
+): void;
 declare function removeEventListener(
   type: string,
-  callback: EventListenerOrEventListenerObject | null,
-  options?: boolean | EventListenerOptions | undefined,
+  listener: EventListenerOrEventListenerObject,
+  options?: boolean | EventListenerOptions,
 ): void;
 
 // TODO(nayeemrmn): Move this to `extensions/web` where its implementation is.

cli/tests/integration/run_tests.rs

@@ -2685,3 +2685,32 @@ itest!(future_check2 {
   output: "future_check2.out",
   envs: vec![("DENO_FUTURE_CHECK".to_string(), "1".to_string())],
 });
+
+itest!(event_listener_error {
+  args: "run --quiet event_listener_error.ts",
+  output: "event_listener_error.ts.out",
+  exit_code: 1,
+});
+
+itest!(event_listener_error_handled {
+  args: "run --quiet event_listener_error_handled.ts",
+  output: "event_listener_error_handled.ts.out",
+});
+
+// https://github.com/denoland/deno/pull/14159#issuecomment-1092285446
+itest!(event_listener_error_immediate_exit {
+  args: "run --quiet event_listener_error_immediate_exit.ts",
+  output: "event_listener_error_immediate_exit.ts.out",
+  exit_code: 1,
+});
+
+itest!(set_timeout_error {
+  args: "run --quiet set_timeout_error.ts",
+  output: "set_timeout_error.ts.out",
+  exit_code: 1,
+});
+
+itest!(set_timeout_error_handled {
+  args: "run --quiet set_timeout_error_handled.ts",
+  output: "set_timeout_error_handled.ts.out",
+});

cli/tests/testdata/event_listener_error.ts

@@ -0,0 +1,6 @@
+addEventListener("foo", () => {
+  throw new Error("bar");
+});
+console.log(1);
+dispatchEvent(new CustomEvent("foo"));
+console.log(2);

cli/tests/testdata/event_listener_error.ts.out

@@ -0,0 +1,7 @@
+1
+error: Uncaught Error: bar
+  throw new Error("bar");
+        ^
+    at [WILDCARD]/event_listener_error.ts:2:9
+    at [WILDCARD]
+    at [WILDCARD]/event_listener_error.ts:5:1

cli/tests/testdata/event_listener_error_handled.ts

@@ -0,0 +1,23 @@
+addEventListener("error", (event) => {
+  console.log({
+    cancelable: event.cancelable,
+    message: event.message,
+    filename: event.filename?.slice?.(-100),
+    lineno: event.lineno,
+    colno: event.colno,
+    error: event.error,
+  });
+  event.preventDefault();
+});
+
+onerror = (event) => {
+  console.log("onerror() called", event.error);
+};
+
+addEventListener("foo", () => {
+  throw new Error("bar");
+});
+
+console.log(1);
+dispatchEvent(new CustomEvent("foo"));
+console.log(2);

cli/tests/testdata/event_listener_error_handled.ts.out

@@ -0,0 +1,17 @@
+1
+{
+  cancelable: true,
+  message: "Uncaught Error: bar",
+  filename: "[WILDCARD]/event_listener_error_handled.ts",
+  lineno: 18,
+  colno: 9,
+  error: Error: bar
+    at [WILDCARD]/event_listener_error_handled.ts:18:9
+    at [WILDCARD]
+    at [WILDCARD]/event_listener_error_handled.ts:22:1
+}
+onerror() called Error: bar
+    at [WILDCARD]/event_listener_error_handled.ts:18:9
+    at [WILDCARD]
+    at [WILDCARD]/event_listener_error_handled.ts:22:1
+2

cli/tests/testdata/event_listener_error_immediate_exit.ts

@@ -0,0 +1,12 @@
+addEventListener("foo", () => {
+  queueMicrotask(() => console.log("queueMicrotask"));
+  setTimeout(() => console.log("timer"), 0);
+  throw new Error("bar");
+});
+console.log(1);
+// @ts-ignore Deno.core
+Deno.core.setNextTickCallback(() => console.log("nextTick"));
+// @ts-ignore Deno.core
+Deno.core.setHasTickScheduled(true);
+dispatchEvent(new CustomEvent("foo"));
+console.log(2);

cli/tests/testdata/event_listener_error_immediate_exit.ts.out

@@ -0,0 +1,6 @@
+1
+error: Uncaught Error: bar
+  throw new Error("bar");
+        ^
+    at [WILDCARD]/event_listener_error_immediate_exit.ts:4:9[WILDCARD]
+    at [WILDCARD]/event_listener_error_immediate_exit.ts:11:1

cli/tests/testdata/set_timeout_error.ts

@@ -0,0 +1,3 @@
+setTimeout(() => {
+  throw new Error("foo");
+}, 0);

cli/tests/testdata/set_timeout_error.ts.out

@@ -0,0 +1,5 @@
+error: Uncaught Error: foo
+  throw new Error("foo");
+        ^
+    at [WILDCARD]/set_timeout_error.ts:2:9
+    at [WILDCARD]

cli/tests/testdata/set_timeout_error_handled.ts

@@ -0,0 +1,19 @@
+addEventListener("error", (event) => {
+  console.log({
+    cancelable: event.cancelable,
+    message: event.message,
+    filename: event.filename?.slice?.(-100),
+    lineno: event.lineno,
+    colno: event.colno,
+    error: event.error,
+  });
+  event.preventDefault();
+});
+
+onerror = (event) => {
+  console.log("onerror() called", event.error);
+};
+
+setTimeout(() => {
+  throw new Error("foo");
+}, 0);

cli/tests/testdata/set_timeout_error_handled.ts.out

@@ -0,0 +1,13 @@
+{
+  cancelable: true,
+  message: "Uncaught Error: foo",
+  filename: "[WILDCARD]/set_timeout_error_handled.ts",
+  lineno: 18,
+  colno: 9,
+  error: Error: foo
+    at [WILDCARD]/set_timeout_error_handled.ts:18:9
+    at [WILDCARD]
+}
+onerror() called Error: foo
+    at [WILDCARD]/set_timeout_error_handled.ts:18:9
+    at [WILDCARD]

cli/tests/testdata/worker_drop_handle_race.js.out

@@ -4,5 +4,5 @@ error: Uncaught (in worker "") Error
     at [WILDCARD]/workers/drop_handle_race.js:2:9
     at Object.action (deno:ext/web/02_timers.js:[WILDCARD])
     at handleTimerMacrotask (deno:ext/web/02_timers.js:[WILDCARD])
-error: Uncaught (in promise) Error: Unhandled error event in child worker.
+error: Uncaught (in promise) Error: Unhandled error in child worker.
     at Worker.#pollControl (deno:runtime/js/11_workers.js:[WILDCARD])

cli/tests/testdata/worker_event_handler_test.js.out

@@ -1,10 +1,10 @@
 Target from self.onmessage: [object DedicatedWorkerGlobalScope]
 Target from message event listener: [object DedicatedWorkerGlobalScope]
 Arguments from self.onerror: [
-  "Some error message",
-  "",
-  0,
-  0,
+  "Uncaught Error: Some error message",
+  "[WILDCARD]/worker_event_handlers.js",
+  9,
+  9,
   Error: Some error message
     at [WILDCARD]
 ]

cli/tests/testdata/workers/nonexistent_worker.out

@@ -1,3 +1,3 @@
 [WILDCARD]error: Uncaught (in worker "") Module not found "file:///[WILDCARD]/workers/doesnt_exist.js".
-error: Uncaught (in promise) Error: Unhandled error event in child worker.
+error: Uncaught (in promise) Error: Unhandled error in child worker.
     at Worker.#pollControl ([WILDCARD])

cli/tests/testdata/workers/permissions_blob_local.ts.out

@@ -1,4 +1,4 @@
 error: Uncaught (in worker "") Requires read access to "[WILDCARD]local_file.ts", run again with the --allow-read flag
     at blob:null/[WILDCARD]:1:8
-error: Uncaught (in promise) Error: Unhandled error event in child worker.
+error: Uncaught (in promise) Error: Unhandled error in child worker.
     at Worker.#pollControl ([WILDCARD])

cli/tests/testdata/workers/permissions_blob_remote.ts.out

@@ -1,4 +1,4 @@
 error: Uncaught (in worker "") Requires net access to "example.com", run again with the --allow-net flag
     at blob:null/[WILDCARD]:1:8
-error: Uncaught (in promise) Error: Unhandled error event in child worker.
+error: Uncaught (in promise) Error: Unhandled error in child worker.
     at Worker.#pollControl ([WILDCARD])

cli/tests/testdata/workers/permissions_data_local.ts.out

@@ -1,4 +1,4 @@
 error: Uncaught (in worker "") Requires read access to "[WILDCARD]local_file.ts", run again with the --allow-read flag
     at data:application/javascript;base64,[WILDCARD]:1:8
-error: Uncaught (in promise) Error: Unhandled error event in child worker.
+error: Uncaught (in promise) Error: Unhandled error in child worker.
     at Worker.#pollControl ([WILDCARD])

cli/tests/testdata/workers/permissions_data_remote.ts.out

@@ -1,4 +1,4 @@
 error: Uncaught (in worker "") Requires net access to "example.com", run again with the --allow-net flag
     at data:application/javascript;base64,aW1wb3J0ICJodHRwczovL2V4YW1wbGUuY29tL3NvbWUvZmlsZS50cyI7:1:8
-error: Uncaught (in promise) Error: Unhandled error event in child worker.
+error: Uncaught (in promise) Error: Unhandled error in child worker.
     at Worker.#pollControl ([WILDCARD])

cli/tests/testdata/workers/permissions_dynamic_remote.ts.out

@@ -2,5 +2,5 @@ error: Uncaught (in worker "") (in promise) TypeError: Requires net access to "e
 await import("https://example.com/some/file.ts");
 ^
     at async http://localhost:4545/workers/dynamic_remote.ts:2:1
-[WILDCARD]error: Uncaught (in promise) Error: Unhandled error event in child worker.
+[WILDCARD]error: Uncaught (in promise) Error: Unhandled error in child worker.
     at Worker.#pollControl ([WILDCARD])

cli/tests/testdata/workers/permissions_remote_remote.ts.out

@@ -1,4 +1,4 @@
 error: Uncaught (in worker "") Requires net access to "example.com", run again with the --allow-net flag
     at http://localhost:4545/workers/static_remote.ts:2:8
-error: Uncaught (in promise) Error: Unhandled error event in child worker.
+error: Uncaught (in promise) Error: Unhandled error in child worker.
     at Worker.#pollControl ([WILDCARD])

cli/tests/testdata/workers/worker_async_error.ts.out

@@ -3,5 +3,5 @@ error: Uncaught (in worker "foo") (in promise) Error: bar
         ^
     at [WILDCARD]/async_error.ts:[WILDCARD]
     at [WILDCARD]/async_error.ts:[WILDCARD]
-error: Uncaught (in promise) Error: Unhandled error event in child worker.
+error: Uncaught (in promise) Error: Unhandled error in child worker.
     at Worker.#pollControl ([WILDCARD])

cli/tests/testdata/workers/worker_error.ts.out

@@ -1,5 +1,5 @@
 [WILDCARD]error: Uncaught (in worker "bar") Error: foo[WILDCARD]
     at foo ([WILDCARD])
     at [WILDCARD]
-error: Uncaught (in promise) Error: Unhandled error event in child worker.
+error: Uncaught (in promise) Error: Unhandled error in child worker.
     at Worker.#pollControl ([WILDCARD])

cli/tests/testdata/workers/worker_message_handler_error.ts.out

@@ -1,7 +1,7 @@
-error: Uncaught (in worker "foo") (in promise) Error: bar
+error: Uncaught (in worker "foo") Error: bar
   throw new Error("bar");
         ^
     at onmessage ([WILDCARD]/message_handler_error.ts:[WILDCARD])
     at [WILDCARD]
-error: Uncaught (in promise) Error: Unhandled error event in child worker.
+error: Uncaught (in promise) Error: Unhandled error in child worker.
     at Worker.#pollControl ([WILDCARD])

cli/tests/testdata/workers/worker_nested_error.ts.out

@@ -3,7 +3,7 @@
         ^
     at foo ([WILDCARD]/workers/error.ts:[WILDCARD])
     at [WILDCARD]/workers/error.ts:[WILDCARD]
-error: Uncaught (in worker "baz") (in promise) Error: Unhandled error event in child worker.
+error: Uncaught (in worker "baz") (in promise) Error: Unhandled error in child worker.
     at Worker.#pollControl ([WILDCARD])
-error: Uncaught (in promise) Error: Unhandled error event in child worker.
+error: Uncaught (in promise) Error: Unhandled error in child worker.
     at Worker.#pollControl ([WILDCARD])

core/bindings.rs

@@ -1,6 +1,7 @@
 // Copyright 2018-2022 the Deno authors. All rights reserved. MIT license.
 
 use crate::error::is_instance_of_error;
+use crate::error::JsError;
 use crate::modules::get_module_type_from_assertions;
 use crate::modules::parse_import_assertions;
 use crate::modules::validate_import_assertions;
@@ -102,6 +103,12 @@ pub static EXTERNAL_REFERENCES: Lazy<v8::ExternalReferences> =
       v8::ExternalReference {
         function: abort_wasm_streaming.map_fn_to(),
       },
+      v8::ExternalReference {
+        function: destructure_error.map_fn_to(),
+      },
+      v8::ExternalReference {
+        function: terminate.map_fn_to(),
+      },
     ])
   });
 
@@ -228,6 +235,8 @@ pub fn initialize_context<'s>(
     set_wasm_streaming_callback,
   );
   set_func(scope, core_val, "abortWasmStreaming", abort_wasm_streaming);
+  set_func(scope, core_val, "destructureError", destructure_error);
+  set_func(scope, core_val, "terminate", terminate);
   // Direct bindings on `window`.
   set_func(scope, global, "queueMicrotask", queue_microtask);
 
@@ -1293,6 +1302,28 @@ fn queue_microtask(
   };
 }
 
+fn destructure_error(
+  scope: &mut v8::HandleScope,
+  args: v8::FunctionCallbackArguments,
+  mut rv: v8::ReturnValue,
+) {
+  let js_error = JsError::from_v8_exception(scope, args.get(0));
+  let object = serde_v8::to_v8(scope, js_error).unwrap();
+  rv.set(object);
+}
+
+fn terminate(
+  scope: &mut v8::HandleScope,
+  args: v8::FunctionCallbackArguments,
+  _rv: v8::ReturnValue,
+) {
+  let state_rc = JsRuntime::state(scope);
+  let mut state = state_rc.borrow_mut();
+  state.explicit_terminate_exception =
+    Some(v8::Global::new(scope, args.get(0)));
+  scope.terminate_execution();
+}
+
 fn create_host_object(
   scope: &mut v8::HandleScope,
   _args: v8::FunctionCallbackArguments,

core/error.rs

@@ -90,7 +90,8 @@ pub fn get_custom_error_class(error: &Error) -> Option<&'static str> {
 /// A `JsError` represents an exception coming from V8, with stack frames and
 /// line numbers. The deno_cli crate defines another `JsError` type, which wraps
 /// the one defined here, that adds source map support and colorful formatting.
-#[derive(Debug, PartialEq, Clone)]
+#[derive(Debug, PartialEq, Clone, serde::Deserialize, serde::Serialize)]
+#[serde(rename_all = "camelCase")]
 pub struct JsError {
   pub message: String,
   pub cause: Option<Box<JsError>>,
@@ -103,7 +104,7 @@ pub struct JsError {
   pub stack: Option<String>,
 }
 
-#[derive(Debug, PartialEq, Clone, serde::Deserialize)]
+#[derive(Debug, PartialEq, Clone, serde::Deserialize, serde::Serialize)]
 #[serde(rename_all = "camelCase")]
 pub struct JsStackFrame {
   pub type_name: Option<String>,
@@ -190,7 +191,6 @@ impl JsError {
 
     let msg = v8::Exception::create_message(scope, exception);
 
-    let (message, frames, stack, cause) =
     if is_instance_of_error(scope, exception) {
       // The exception is a JS Error object.
       let exception: v8::Local<v8::Object> = exception.try_into().unwrap();
@@ -235,24 +235,9 @@ impl JsError {
 
       // Convert them into Vec<JsStackFrame>
       let frames: Vec<JsStackFrame> = match frames_v8 {
-          Some(frames_v8) => {
-            serde_v8::from_v8(scope, frames_v8.into()).unwrap()
-          }
+        Some(frames_v8) => serde_v8::from_v8(scope, frames_v8.into()).unwrap(),
         None => vec![],
       };
-        (message, frames, stack, cause)
-      } else {
-        // The exception is not a JS Error object.
-        // Get the message given by V8::Exception::create_message(), and provide
-        // empty frames.
-        (
-          msg.get(scope).to_rust_string_lossy(scope),
-          vec![],
-          None,
-          None,
-        )
-      };
-
       Self {
         message,
         cause,
@@ -269,6 +254,22 @@ impl JsError {
         frames,
         stack,
       }
+    } else {
+      // The exception is not a JS Error object.
+      // Get the message given by V8::Exception::create_message(), and provide
+      // empty frames.
+      Self {
+        message: msg.get(scope).to_rust_string_lossy(scope),
+        cause: None,
+        script_resource_name: None,
+        source_line: None,
+        line_number: None,
+        start_column: None,
+        end_column: None,
+        frames: vec![],
+        stack: None,
+      }
+    }
   }
 }
 
@@ -337,6 +338,9 @@ pub(crate) fn is_instance_of_error<'s>(
   let mut maybe_prototype =
     value.to_object(scope).unwrap().get_prototype(scope);
   while let Some(prototype) = maybe_prototype {
+    if !prototype.is_object() {
+      return false;
+    }
     if prototype.strict_equals(error_prototype) {
       return true;
     }

core/runtime.rs

@@ -169,6 +169,10 @@ pub(crate) struct JsRuntimeState {
   pub(crate) op_ctxs: Box<[OpCtx]>,
   pub(crate) shared_array_buffer_store: Option<SharedArrayBufferStore>,
   pub(crate) compiled_wasm_module_store: Option<CompiledWasmModuleStore>,
+  /// The error that was passed to an explicit `Deno.core.terminate` call.
+  /// It will be retrieved by `exception_to_err_result` and used as an error
+  /// instead of any other exceptions.
+  pub(crate) explicit_terminate_exception: Option<v8::Global<v8::Value>>,
   waker: AtomicWaker,
 }
 
@@ -384,6 +388,7 @@ impl JsRuntime {
       op_state: op_state.clone(),
       op_ctxs,
       have_unpolled_ops: false,
+      explicit_terminate_exception: None,
       waker: AtomicWaker::new(),
     })));
 
@@ -1017,19 +1022,33 @@ pub(crate) fn exception_to_err_result<'s, T>(
   exception: v8::Local<v8::Value>,
   in_promise: bool,
 ) -> Result<T, Error> {
+  let state_rc = JsRuntime::state(scope);
+  let mut state = state_rc.borrow_mut();
+
   let is_terminating_exception = scope.is_execution_terminating();
   let mut exception = exception;
 
   if is_terminating_exception {
-    // TerminateExecution was called. Cancel exception termination so that the
+    // TerminateExecution was called. Cancel isolate termination so that the
     // exception can be created..
     scope.cancel_terminate_execution();
 
+    // If the termination is the result of a `Deno.core.terminate` call, we want
+    // to use the exception that was passed to it rather than the exception that
+    // was passed to this function.
+    exception = state
+      .explicit_terminate_exception
+      .take()
+      .map(|exception| v8::Local::new(scope, exception))
+      .unwrap_or_else(|| {
         // Maybe make a new exception object.
         if exception.is_null_or_undefined() {
           let message = v8::String::new(scope, "execution terminated").unwrap();
-      exception = v8::Exception::error(scope, message);
+          v8::Exception::error(scope, message)
+        } else {
+          exception
         }
+      });
   }
 
   let mut js_error = JsError::from_v8_exception(scope, exception);
@@ -1039,9 +1058,6 @@ pub(crate) fn exception_to_err_result<'s, T>(
       js_error.message.trim_start_matches("Uncaught ")
     );
   }
-
-  let state_rc = JsRuntime::state(scope);
-  let state = state_rc.borrow();
   let js_error = (state.js_error_create_fn)(js_error);
 
   if is_terminating_exception {
@@ -1222,7 +1238,14 @@ impl JsRuntime {
     // Update status after evaluating.
     status = module.get_status();
 
-    if let Some(value) = maybe_value {
+    let explicit_terminate_exception =
+      state_rc.borrow_mut().explicit_terminate_exception.take();
+    if let Some(exception) = explicit_terminate_exception {
+      let exception = v8::Local::new(tc_scope, exception);
+      sender
+        .send(exception_to_err_result(tc_scope, exception, false))
+        .expect("Failed to send module evaluation error.");
+    } else if let Some(value) = maybe_value {
       assert!(
         status == v8::ModuleStatus::Evaluated
           || status == v8::ModuleStatus::Errored

ext/web/02_event.js

@@ -7,6 +7,7 @@
 "use strict";
 
 ((window) => {
+  const core = window.Deno.core;
   const webidl = window.__bootstrap.webidl;
   const { DOMException } = window.__bootstrap.domException;
   const consoleInternal = window.__bootstrap.console;
@@ -32,6 +33,7 @@
     ObjectPrototypeIsPrototypeOf,
     ReflectDefineProperty,
     SafeArrayIterator,
+    StringPrototypeStartsWith,
     Symbol,
     SymbolFor,
     SymbolToStringTag,
@@ -787,7 +789,11 @@
 
     setCurrentTarget(eventImpl, tuple.item);
 
+    try {
       innerInvokeEventListeners(eventImpl, getListeners(tuple.item));
+    } catch (error) {
+      reportException(error);
+    }
   }
 
   function normalizeAddEventHandlerOptions(
@@ -1317,6 +1323,49 @@
     });
   }
 
+  let reportExceptionStackedCalls = 0;
+
+  // https://html.spec.whatwg.org/#report-the-exception
+  function reportException(error) {
+    reportExceptionStackedCalls++;
+    const jsError = core.destructureError(error);
+    const message = jsError.message;
+    let filename = "";
+    let lineno = 0;
+    let colno = 0;
+    if (jsError.frames.length > 0) {
+      filename = jsError.frames[0].fileName;
+      lineno = jsError.frames[0].lineNumber;
+      colno = jsError.frames[0].columnNumber;
+    } else {
+      const jsError = core.destructureError(new Error());
+      for (const frame of jsError.frames) {
+        if (
+          typeof frame.fileName == "string" &&
+          !StringPrototypeStartsWith(frame.fileName, "deno:")
+        ) {
+          filename = frame.fileName;
+          lineno = frame.lineNumber;
+          colno = frame.columnNumber;
+          break;
+        }
+      }
+    }
+    const event = new ErrorEvent("error", {
+      cancelable: true,
+      message,
+      filename,
+      lineno,
+      colno,
+      error,
+    });
+    // Avoid recursing `reportException()` via error handlers more than once.
+    if (reportExceptionStackedCalls > 1 || window.dispatchEvent(event)) {
+      core.terminate(error);
+    }
+    reportExceptionStackedCalls--;
+  }
+
   window.Event = Event;
   window.EventTarget = EventTarget;
   window.ErrorEvent = ErrorEvent;
@@ -1333,6 +1382,7 @@
     listenerCount,
   };
   window.__bootstrap.event = {
+    reportException,
     setIsTrusted,
     setTarget,
     defineEventHandler,

ext/web/02_timers.js

@@ -21,6 +21,7 @@
     TypeError,
   } = window.__bootstrap.primordials;
   const { webidl } = window.__bootstrap;
+  const { reportException } = window.__bootstrap.event;
   const { assert } = window.__bootstrap.infra;
 
   function opNow() {
@@ -139,13 +140,16 @@
 
         // 2.
         // 3.
-        // TODO(@andreubotella): Error handling.
         if (typeof callback === "function") {
+          try {
             FunctionPrototypeCall(
               callback,
               globalThis,
               ...new SafeArrayIterator(args),
             );
+          } catch (error) {
+            reportException(error);
+          }
         } else {
           // TODO(@andreubotella): eval doesn't seem to have a primordial, but
           // it can be redefined in the global scope.

runtime/js/11_workers.js

@@ -140,14 +140,16 @@
         error: null,
       });
 
-      let handled = false;
-
       this.dispatchEvent(event);
-      if (event.defaultPrevented) {
-        handled = true;
+      // Don't bubble error event to window for loader errors (`!e.fileName`).
+      // TODO(nayeemrmn): Currently these are never bubbled because worker
+      // error event fields aren't populated correctly and `e.fileName` is
+      // always empty.
+      if (e.fileName && !event.defaultPrevented) {
+        window.dispatchEvent(event);
       }
 
-      return handled;
+      return event.defaultPrevented;
     }
 
     #pollControl = async () => {
@@ -165,7 +167,7 @@
           } /* falls through */
           case 2: { // Error
             if (!this.#handleError(data)) {
-              throw new Error("Unhandled error event in child worker.");
+              throw new Error("Unhandled error in child worker.");
             }
             break;
           }

runtime/js/99_main.js

@@ -558,6 +558,7 @@ delete Object.prototype.__proto__;
 
     eventTarget.setEventTargetData(globalThis);
 
+    defineEventHandler(window, "error");
     defineEventHandler(window, "load");
     defineEventHandler(window, "unload");
 

runtime/web_worker.rs

@@ -119,6 +119,7 @@ pub struct WebWorkerInternalHandle {
   has_terminated: Arc<AtomicBool>,
   terminate_waker: Arc<AtomicWaker>,
   isolate_handle: v8::IsolateHandle,
+  pub name: String,
   pub worker_type: WebWorkerType,
 }
 
@@ -264,6 +265,7 @@ impl WebWorkerHandle {
 
 fn create_handles(
   isolate_handle: v8::IsolateHandle,
+  name: String,
   worker_type: WebWorkerType,
 ) -> (WebWorkerInternalHandle, SendableWebWorkerHandle) {
   let (parent_port, worker_port) = create_entangled_message_port();
@@ -272,13 +274,14 @@ fn create_handles(
   let has_terminated = Arc::new(AtomicBool::new(false));
   let terminate_waker = Arc::new(AtomicWaker::new());
   let internal_handle = WebWorkerInternalHandle {
-    sender: ctrl_tx,
+    name,
     port: Rc::new(parent_port),
     termination_signal: termination_signal.clone(),
     has_terminated: has_terminated.clone(),
     terminate_waker: terminate_waker.clone(),
     isolate_handle: isolate_handle.clone(),
     cancel: CancelHandle::new_rc(),
+    sender: ctrl_tx,
     worker_type,
   };
   let external_handle = SendableWebWorkerHandle {
@@ -452,7 +455,7 @@ impl WebWorker {
     let (internal_handle, external_handle) = {
       let handle = js_runtime.v8_isolate().thread_safe_handle();
       let (internal_handle, external_handle) =
-        create_handles(handle, options.worker_type);
+        create_handles(handle, name.clone(), options.worker_type);
       let op_state = js_runtime.op_state();
       let mut op_state = op_state.borrow_mut();
       op_state.put(internal_handle.clone());

runtime/worker.rs

@@ -217,6 +217,10 @@ impl MainWorker {
   async fn evaluate_module(&mut self, id: ModuleId) -> Result<(), AnyError> {
     let mut receiver = self.js_runtime.mod_evaluate(id);
     tokio::select! {
+      // Not using biased mode leads to non-determinism for relatively simple
+      // programs.
+      biased;
+
       maybe_result = &mut receiver => {
         debug!("received module evaluate {:#?}", maybe_result);
         maybe_result.expect("Module evaluation result not provided.")