feat: "rejectionhandled" Web event and "rejectionHandled" Node event (#21875)

This commit adds support for "rejectionhandled" Web Event and
"rejectionHandled" Node event.

```js
import process from "node:process";

process.on("rejectionHandled", (promise) => {
  console.log("rejectionHandled", reason, promise);
});

window.addEventListener("rejectionhandled", (event) => {
  console.log("rejectionhandled", event.reason, event.promise);
});
```

---------

Co-authored-by: Matt Mastracci <matthew@mastracci.com>

1 files changed, 17 insertions, 1 deletions

diff --git a/ext/node/polyfills/process.ts b/ext/node/polyfills/process.ts
index 3d5009b90..1edcccc00 100644
--- a/ext/node/polyfills/process.ts
+++ b/ext/node/polyfills/process.ts
@@ -75,7 +75,6 @@ import { buildAllowedFlags } from "ext:deno_node/internal/process/per_thread.mjs
 
 const notImplementedEvents = [
   "multipleResolves",
-  "rejectionHandled",
   "worker",
 ];
 
@@ -746,6 +745,7 @@ export const removeListener = process.removeListener;
 export const removeAllListeners = process.removeAllListeners;
 
 let unhandledRejectionListenerCount = 0;
+let rejectionHandledListenerCount = 0;
 let uncaughtExceptionListenerCount = 0;
 let beforeExitListenerCount = 0;
 let exitListenerCount = 0;
@@ -755,6 +755,9 @@ process.on("newListener", (event: string) => {
     case "unhandledRejection":
       unhandledRejectionListenerCount++;
       break;
+    case "rejectionHandled":
+      rejectionHandledListenerCount++;
+      break;
     case "uncaughtException":
       uncaughtExceptionListenerCount++;
       break;
@@ -775,6 +778,9 @@ process.on("removeListener", (event: string) => {
     case "unhandledRejection":
       unhandledRejectionListenerCount--;
       break;
+    case "rejectionHandled":
+      rejectionHandledListenerCount--;
+      break;
     case "uncaughtException":
       uncaughtExceptionListenerCount--;
       break;
@@ -837,6 +843,16 @@ function synchronizeListeners() {
     internals.nodeProcessUnhandledRejectionCallback = undefined;
   }
 
+  // Install special "handledrejection" handler, that will be called
+  // last.
+  if (rejectionHandledListenerCount > 0) {
+    internals.nodeProcessRejectionHandledCallback = (event) => {
+      process.emit("rejectionHandled", event.reason, event.promise);
+    };
+  } else {
+    internals.nodeProcessRejectionHandledCallback = undefined;
+  }
+
   if (uncaughtExceptionListenerCount > 0) {
     globalThis.addEventListener("error", processOnError);
   } else {