How to workaround non-existent onunhandledrejection in Adobe UXP (Javascript)

[jardicc]

Adobe has UXP technology for its plugins. It looks like a web browser but it is not. It looks like NodeJS but it not either. But it includes whole V8 engine.

I can add Sentry for Browser. I can also explicitly send an error calling sentry function and it works. But it does not catch unhadled rejections automatically. Because onunhandledrejection is not implemented in UXP.

Sentry listents to that event but UXP will never fire it. Also unhandled rejection is never logged into console by default. I have to use try/catch and rethrow it myslef.

Is there some a way to workaround it? I was thinking maybe to intercept Error constructor or something like that but it did not work. And Error.captureStackTrace is called in so many non-error cases that I cannot use it.

I can wrap top level code into try/catch call Sentry explicitly and it works for awaited child functions but if some nested promise is not awaited then it is not catched and error not reported.

[AbhiPrasad]

@jardicc unfortunately I think without the hook being implemented we can't do much to catch unhandled errors automatically. In addition, with onunhandledrejection, isn't there the danger that non-plugin related errors could get captured as well? Therefore you could be sending non-application related code to Sentry.

For now I recommend just manually wrapping code and calling Sentry explicitly, that will at least give you some coverage.

Note: There is an extremely hacky approach for this, which is to patch the global Promise object and hook into Promise.catch. I don't recommend this, but this also will make sure errors get reported to Sentry.

[jardicc]

Thanks for advice. I will try lobbying in Adobe for adding onunhandledrejection

(for reference: https://forums.creativeclouddeveloper.com/t/errors-not-shown-how-to-workaround-non-existent-onunhandledrejection/7967/4 )

[jardicc]

@AbhiPrasad would you have any hints on how to do the Promise.catch hack? Even if I would not ship this in production... having this in development available would be very valuable.

[AbhiPrasad]

something like so:

globalThis.Promise.prototype.catch = new Proxy(
  globalThis.Promise.prototype.catch,
  {
    apply(target, thisArg, catchArgs) {
      console.log("Promise.prototype.catch called");
      catchArgs[0] = new Proxy(catchArgs[0], {
        apply(target, thisArg, callbackArgs) {
          // callbackArgs[0] is the error passed to the catch callback
          console.log(
            "Promise.prototype.catch callback called with error:\n",
            callbackArgs[0]
          );
          // Sentry.captureException(callbackArgs[0]);
          return target.apply(thisArg, callbackArgs);
        },
      });
      return target.apply(thisArg, catchArgs);
    },
  }
);

new Promise((_, reject) => {
  reject(new Error("Promise rejected"));
}).catch((e) => {
  // do nothing
});

It's a brittle monkeypatch, there might be edge cases I'm missing, but overall should work.

[jardicc]

Thanks! I will experiment with it.

Meanwhile I found: https://github.com/rtsao/browser-unhandled-rejection
It worked in web browser but I could not make it work in UXP without obvious reason for failure.

[AbhiPrasad]

The polyfill only triggers if typeof PromiseRejectionEvent === 'undefined' returns true. Try running that and seeing what gets logged out.

Another thing with this polyfill is that it replaces Promise directly, which may not work if they've frozen the Promise in UXP settings (so Promise = InstrumentedPromise becomes a no-op).

[jardicc]

It is not frozen and the check returns true. But the thing I did wrong... it could be anything... it could be even UXP internals.