Add exception handling for microtasks and nextTick callbacks

src/bun.js/event_loop.zig

@@ -113,6 +113,12 @@ pub fn drainMicrotasksWithGlobal(this: *EventLoop, globalObject: *JSC.JSGlobalOb
     jsc_vm.releaseWeakRefs();
     JSC__JSGlobalObject__drainMicrotasks(globalObject);
 
+    // Check if an exception was thrown during microtask execution
+    if (globalObject.hasException()) {
+        // Report the exception as unhandled - this will clear the exception and report it
+        globalObject.reportActiveExceptionAsUnhandled(error.JSError);
+    }
+
     this.virtual_machine.is_inside_deferred_task_queue = true;
     this.deferred_tasks.run();
     this.virtual_machine.is_inside_deferred_task_queue = false;

test/js/web/timers/microtask-exception.test.js

@@ -0,0 +1,75 @@
+import { it, expect } from "bun:test";
+
+it("queueMicrotask exception handling", async () => {
+  // Test that exceptions in microtasks are properly reported and don't crash
+  const errors = [];
+  const originalOnError = globalThis.onerror;
+
+  // Set up error handler to capture unhandled exceptions
+  globalThis.onerror = (message, source, lineno, colno, error) => {
+    errors.push({ message, error });
+    return true; // Prevent default error handling
+  };
+
+  try {
+    await new Promise(resolve => {
+      let microtaskRan = false;
+
+      // Queue a microtask that throws
+      queueMicrotask(() => {
+        throw new Error("Exception from microtask!");
+      });
+
+      // Queue another microtask to verify execution continues
+      queueMicrotask(() => {
+        microtaskRan = true;
+      });
+
+      // Wait a bit for microtasks to run
+      setTimeout(() => {
+        expect(microtaskRan).toBe(true);
+        expect(errors.length).toBeGreaterThan(0);
+        expect(errors[0].error.message).toBe("Exception from microtask!");
+        resolve();
+      }, 10);
+    });
+  } finally {
+    // Restore original error handler
+    globalThis.onerror = originalOnError;
+  }
+});
+
+it("process.nextTick exception handling", async () => {
+  // Test that exceptions in nextTick callbacks are properly reported
+  const errors = [];
+  const originalOnError = globalThis.onerror;
+
+  globalThis.onerror = (message, source, lineno, colno, error) => {
+    errors.push({ message, error });
+    return true;
+  };
+
+  try {
+    await new Promise(resolve => {
+      let nextTickRan = false;
+
+      // Use nextTick which also uses the microtask queue
+      process.nextTick(() => {
+        throw new Error("Exception from nextTick!");
+      });
+
+      process.nextTick(() => {
+        nextTickRan = true;
+      });
+
+      setTimeout(() => {
+        expect(nextTickRan).toBe(true);
+        expect(errors.length).toBeGreaterThan(0);
+        expect(errors[0].error.message).toBe("Exception from nextTick!");
+        resolve();
+      }, 10);
+    });
+  } finally {
+    globalThis.onerror = originalOnError;
+  }
+});