[0.73] Remote JS Debugging deprecation

[huntie]

Introduction

In React Native 0.73, we are deprecating Remote JavaScript Debugging via Chrome (docs).

Remote JavaScript Debugging was previously the default debugging experience for apps using JavaScriptCore (JSC). It involves switching JavaScript execution into an external V8 process, to debug in the Chrome browser.

Motivation

• The model of switching JS execution into a separate V8 process is inconsistent with how users' apps actually run. Things such as interactions with Native Modules were in a broken state. In particular, we noticed Remote JS Debugging being incompatible with the New Architecture.
• As the React Native team continues to invest in improving debugging, we want to reduce the surface area of debugging modes that we support.

We are focusing future debugging efforts into providing a first-class experience for Hermes.

Alternatives

• We recommend using Hermes for a consistent debugging experience on all platforms. See all supported debugging methods under Opening the Debugger.
• We recommend Safari Developer Tools (direct JSC debugging) instead, for iOS apps using JSC.

Discussion points

• How does this impact third party tooling (which might inform our removal timeline).
• General feedback.

[thymikee]

I welcome this change very much! Many developers I interacted with didn't even realize that "remote debugging" is running V8 instead of the device's JS engine (I guess the notion of a "JS engine" is also foreign to many developers). And they only learned the difference after bumping into a date issue between JSC and V8 to something of that sort

[jamonholmgren]

I agree; I think the new RN JS Inspector will be a much better DX than the remote JS Debugger.

But -- I did appreciate having the Remote JS Debugger as an option. It did help me solve some things in the past! Just time for it to go I think.

[jehillert]

It's great that the future debugging experience looks bright. But deprecating the remote debugging has caused a lot of pain. There are posts all over from folks having no way to use the classic redux-devtools and react-native debugger. Yes, I am aware remote debugging can be turned back on manually, but then there are bugs blocking people from doing so. The fixes may be "easy", but clearly not easy enough because I just joined a team of 30 RN devs who didn't even realize it was still available. And also... for such critically important functionality, its confounding that we have to use patch package to get it working again (re async Hermes error).

The experimental debugger has not been an acceptable substitute. I have a little logger that pretty prints colored objects. I've been using it for years in chrome console. It won't work because the experimental debugger has a bug that prevents pretty printing JSON.stringified objects. So in addition to there being major functionality missing, like network calls, it still struggles with a basic console.log.

And Flipper was not a good choice for a hold-me-over, considering it's deprecated too and the reasons for which it is deprecated. I am happy to see it go... except what the heck? What are we supposed to use? Reactotron?

Redux devtools and react-native-debugger are insanely useful. Maybe not as pretty as the competition, but something many of us relied on heavily because it just does what it does perfectly. It is without equal. To have that taken away, we feel we have been left hanging... It really is surprising too, when I think of how many major commercial decisions must have been made to go with redux because of those devtools.

My point in saying all this is not to offend anyone. If anything, I am appreciative of the opportunities RN has provided me in my career. But it is to say I think the impact of deprecation has been greatly underestimated and it would be really unfortunate if remote debugging was taken out a second before it absolutely has to be. If anything, it should be restored to previous health until the new tooling is mature. It doesn't seem like much work would be required to do so.

[huntie]

@jehillert Thanks for your input. Two immediate things (in lieu of a longer reply I will locate on the feedback thread):

• Support for popular JavaScript library developer tools, such as Redux, is in our known problem space for debugging — but we can't prioritise this work until we launch our next-gen debugger stack (FYI: this is a considerable end-to-end rewrite, and different from today's experimental debugger). We are all-in on Chrome DevTools Protocol and the Chrome DevTools frontend as our debugger host — this does provide a suitable model for hosting other dev plugins, and having them reliably connect to the app's JS runtime, and have internally begun validating this.
  • Today, Expo DevTools Plugins provide the closest thing to working Chrome extensions without using Remote Debugging (although these do NOT currently use CDP).
• We will leave Remote JS Debugging deprecated, but not remove it until we have an full alternative ready for the community.

If you have any more feedback, consider adding to this reply and I'll try to respond and share future updates from the team 🙏🏻.

[jehillert]

We will leave Remote JS Debugging deprecated, but not remove it until we have an full alternative ready for the community.

This is good to hear. The official RN documentation just says it "will be removed in a future release".

[jehillert]

Btw, it was 4:00 AM when I wrote that. The reality is I make all my money using the technology you guys created. Me and half a million other developers. I'm appreciative.