3 files changed, 48 insertions, 10 deletions

diff --git a/cli/tests/integration/watcher_tests.rs b/cli/tests/integration/watcher_tests.rs
index dee198740..b69379427 100644
--- a/cli/tests/integration/watcher_tests.rs
+++ b/cli/tests/integration/watcher_tests.rs
@@ -1038,6 +1038,40 @@ fn test_watch_module_graph_error_referrer() {
   check_alive_then_kill(child);
 }
 
+// Regression test for https://github.com/denoland/deno/issues/15428.
+#[test]
+fn test_watch_unload_handler_error_on_drop() {
+  let t = TempDir::new();
+  let file_to_watch = t.path().join("file_to_watch.js");
+  write(
+    &file_to_watch,
+    r#"
+    addEventListener("unload", () => {
+      throw new Error("foo");
+    });
+    setTimeout(() => {
+      throw new Error("bar");
+    });
+    "#,
+  )
+  .unwrap();
+  let mut child = util::deno_cmd()
+    .current_dir(util::testdata_path())
+    .arg("run")
+    .arg("--watch")
+    .arg(&file_to_watch)
+    .env("NO_COLOR", "1")
+    .stdout(std::process::Stdio::piped())
+    .stderr(std::process::Stdio::piped())
+    .spawn()
+    .unwrap();
+  let (_, mut stderr_lines) = child_lines(&mut child);
+  wait_contains("Process started", &mut stderr_lines);
+  wait_contains("Uncaught Error: bar", &mut stderr_lines);
+  wait_contains("Process finished", &mut stderr_lines);
+  check_alive_then_kill(child);
+}
+
 #[test]
 fn run_watch_dynamic_imports() {
   let t = TempDir::new();
diff --git a/cli/worker.rs b/cli/worker.rs
index 9eae6709b..e766ec4aa 100644
--- a/cli/worker.rs
+++ b/cli/worker.rs
@@ -125,13 +125,18 @@ impl CliMainWorker {
         self.pending_unload = true;
 
         let result = loop {
-          let result = self.inner.worker.run_event_loop(false).await;
-          if !self
+          match self.inner.worker.run_event_loop(false).await {
+            Ok(()) => {}
+            Err(error) => break Err(error),
+          }
+          match self
             .inner
             .worker
-            .dispatch_beforeunload_event(&located_script_name!())?
+            .dispatch_beforeunload_event(&located_script_name!())
           {
-            break result;
+            Ok(default_prevented) if default_prevented => {} // continue loop
+            Ok(_) => break Ok(()),
+            Err(error) => break Err(error),
           }
         };
         self.pending_unload = false;
@@ -152,11 +157,10 @@ impl CliMainWorker {
     impl Drop for FileWatcherModuleExecutor {
       fn drop(&mut self) {
         if self.pending_unload {
-          self
+          let _ = self
             .inner
             .worker
-            .dispatch_unload_event(&located_script_name!())
-            .unwrap();
+            .dispatch_unload_event(&located_script_name!());
         }
       }
     }
diff --git a/core/runtime.rs b/core/runtime.rs
index 5b3b0ce50..42496b271 100644
--- a/core/runtime.rs
+++ b/core/runtime.rs
@@ -1167,11 +1167,11 @@ pub(crate) fn exception_to_err_result<'s, T>(
     // If termination is the result of a `op_dispatch_exception` call, we want
     // to use the exception that was passed to it rather than the exception that
     // was passed to this function.
-    let mut state = state_rc.borrow_mut();
+    let state = state_rc.borrow();
     exception = state
       .dispatched_exceptions
-      .pop_back()
-      .map(|exception| v8::Local::new(scope, exception))
+      .back()
+      .map(|exception| v8::Local::new(scope, exception.clone()))
       .unwrap_or_else(|| {
         // Maybe make a new exception object.
         if was_terminating_execution && exception.is_null_or_undefined() {