use Deno.core.eventLoopHasMoreWork()

node/_core.ts

@@ -22,5 +22,8 @@ if (Deno?.core) {
     encode(chunk: string): Uint8Array {
       return new TextEncoder().encode(chunk);
     },
+    eventLoopHasMoreWork(): boolean {
+      return false;
+    },
   };
 }

node/process.ts

@@ -36,6 +36,8 @@ import {
   stdin as stdin_,
   stdout as stdout_,
 } from "./_process/streams.mjs";
+import { core } from "./_core.ts";
+
 // TODO(kt3k): Give better types to stdio objects
 // deno-lint-ignore no-explicit-any
 const stderr = stderr_ as any;
@@ -81,7 +83,7 @@ export const exit = (code?: number | string) => {
   if (!process._exiting) {
     process._exiting = true;
     // FIXME(bartlomieju): this is wrong, we won't be using syscall to exit
-    // and thus the `unload` event will be emitted to properly trigget "emit"
+    // and thus the `unload` event will not be emitted to properly trigger "emit"
     // event on `process`.
     process.emit("exit", process.exitCode || 0);
   }
@@ -260,8 +262,11 @@ class Process extends EventEmitter {
   constructor() {
     super();
 
-    globalThis.addEventListener("beforeunload", () => {
+    globalThis.addEventListener("beforeunload", (e) => {
       super.emit("beforeExit", process.exitCode || 0);
+      if (core.eventLoopHasMoreWork()) {
+        e.preventDefault();
+      }
     });
 
     globalThis.addEventListener("unload", () => {

process.js

@@ -1,9 +1,9 @@
-process.on('beforeExit', (code) => {
-  console.log('Process beforeExit event with code: ', code);
+process.on("beforeExit", (code) => {
+  console.log("Process beforeExit event with code: ", code);
 });
 
-process.on('exit', (code) => {
-  console.log('Process exit event with code: ', code);
+process.on("exit", (code) => {
+  console.log("Process exit event with code: ", code);
 });
 
-console.log('This message is displayed first.');
+console.log("This message is displayed first.");