feat: add "unhandledrejection" event support (#12994)

This commit adds support for "unhandledrejection" event.

This event will trigger event listeners registered using:

"globalThis.addEventListener("unhandledrejection")
"globalThis.onunhandledrejection"
This is done by registering a default handler using
"Deno.core.setPromiseRejectCallback" that allows to
handle rejected promises in JavaScript instead of Rust.

This commit will make it possible to polyfill
"process.on("unhandledRejection")" in the Node compat
layer.

Co-authored-by: Colin Ihrig <cjihrig@gmail.com>

1 files changed, 1 insertions, 9 deletions

diff --git a/core/bindings.rs b/core/bindings.rs
index a88e54af7..47632d00d 100644
--- a/core/bindings.rs
+++ b/core/bindings.rs
@@ -282,14 +282,6 @@ pub extern "C" fn promise_reject_callback(message: v8::PromiseRejectMessage) {
   let state_rc = JsRuntime::state(scope);
   let mut state = state_rc.borrow_mut();
 
-  // Node compat: perform synchronous process.emit("unhandledRejection").
-  //
-  // Note the callback follows the (type, promise, reason) signature of Node's
-  // internal promiseRejectHandler from lib/internal/process/promises.js, not
-  // the (promise, reason) signature of the "unhandledRejection" event listener.
-  //
-  // Short-circuits Deno's regular unhandled rejection logic because that's
-  // a) asynchronous, and b) always terminates.
   if let Some(js_promise_reject_cb) = state.js_promise_reject_cb.clone() {
     let js_uncaught_exception_cb = state.js_uncaught_exception_cb.clone();
     drop(state); // Drop borrow, callbacks can call back into runtime.
@@ -323,6 +315,7 @@ pub extern "C" fn promise_reject_callback(message: v8::PromiseRejectMessage) {
     }
 
     if tc_scope.has_caught() {
+      // TODO(bartlomieju): ensure that TODO provided below is still valid.
       // If we get here, an exception was thrown by the unhandledRejection
       // handler and there is ether no uncaughtException handler or the
       // handler threw an exception of its own.
@@ -340,7 +333,6 @@ pub extern "C" fn promise_reject_callback(message: v8::PromiseRejectMessage) {
   } else {
     let promise = message.get_promise();
     let promise_global = v8::Global::new(scope, promise);
-
     match message.get_event() {
       PromiseRejectWithNoHandler => {
         let error = message.get_value().unwrap();