Completion roadmap for react-scripts@2.0

[Timer]

Hey everyone! We know progress on react-scripts@2.0 has been stagnating for a while.

We put together a lofty set of goals when we first started v2.
The scope of these changes have proven themselves to be too large to effectively polish everything and create a stable build.

To remediate this, we're going to reduce the scope of v2, polish completed features, and release v2 as stable within the next two (2) weeks.

Action Plan

Our proposed plan of action is as follows (in no particular order):

1. ✅ Fix vendor chunking (Case against enabling AutomaticCommonsChunksPlugin in webpack by default #4977, react-scripts v2 webpack 4 splitChunks name setting should use the default #4769, An explanation of my magically shrinking build size with subsequent alpha builds  #4633, Make chunking toggleable #4632)

   • Vendor chunking exhibits undesirable behavior when used in combination with code splitting. The application dependencies used by every application chunk end up in a single vendor bundle, effectively nullifying the value of code splitting.
   • We would like to create a vendor chunk per application chunk. If this behavior cannot be achieved, we will revert vendoring and place dependencies in the application chunks.
   • As an alternative to the former, we may only enable the vendor chunk when no code splitting is used in your application (if possible).

2. ✅ Switch to Terser (Cannot turn off es5 compile #4948, @next runs out of memory on build, throws JS stacktracke #4902, Consider switching to terser #4711, disable reduce_vars in uglify-es due to bug in code generation #4692, CRA generating invalid sourcemaps? #4683, CRA 2 browserslist build can generate invalid code #4665, Reconsider whether it's safe to rely on recent Uglify versions #4329, Preserve Licenses #4116, String is modified in the production build #4100)

   • Uglify-ES has been the source of a lot of problems, and is no longer maintained. We should switch to Terser (the more maintained fork of Uglify-ES) to fix obscure bugs resulting from production builds.

3. ✅ Revert monoreport support (Add support for yarn and lerna monorepos. #3741, Use yarn when running inside yarn workspace. #3997, Add support for new yarn workspaces config format #4001) because there's too many issues (react-scripts 2.0 breaks some monorepos #4569, jest runs all tests found in monorepo react-scripts@2.0.0-next #4410, next@b2fd8db8 throws if monorepo with nwb modules #4249, RFC: Source Packages #4092, Require monorepo source workspace packages to be opted in via glob. #4570, Can't use a CRA project inside Yarn Workspaces #3031, Support running create-react-app inside a monorepo. #3967)

   • We would've loved to figure out all of the ergonomics around monorepo support, but it turns out it's just too difficult.
   • We're going to revert monorepo support in favor of consuming library packages via nwb and provide excellent documentation on how to do so. This is arguably the best way.

4. ✅ Fix edge-cases for compiling node_modules and polish Babel 7 upgrade

   • Compiling node_modules has surfaced some issues, particularly around async/await and regenerator.
   • We also need to make sure all of our Babel configuration tricks are valid for v7.

5. ✅ Remove mjs support

   • The ecosystem is not ready for mjs support and we're going to remove support to fix complex edge cases with resolving modules. There are alternative resolve orders based on source file and supported features which are concepts Jest does not have support for yet.
   • This will be added back in the future.

6. ✅ Drop advanced proxy configuration and replace it with express middleware

   • Allowing users to configure their proxy in package json has been a pain-point and source of configuration, going against our values of convention.
   • We will remove the ability to configure the proxy and replace it with exposing the express app instance. You can attach any middleware or routes to this express app that you'd like.
   • A recipe for proxying requests will be provided in the documentation.

7. ✅ Remove support for targeting newer browsers

   • We added support for targeting specific sets of browsers and there has been multiple issues that cropped up about this. We are going to remove the ability to target browsers and compile everything down to ES5 -- this is in line with v1 behavior.
   • The difference now is that we compile node_modules, so you can consume any package using newer syntax without worry.
   • In a follow up release, (potentially v2.1) we will explore adding a "modern"/evergreen browser mode which outputs modern, (nearly) uncompiled ESnext. This should give users the best of both worlds, and is in line with what we see in the community. A proposal going into more detail will be put together after the release of v2.

How can I help?

Please let us know your thoughts and if we missed anything.
We'll be more than happy to explain our rationale around these decisions if there's any further questions.

If there's anything you (and the community) feel strongly about but is not found on this list, please make an effort to send a PR!
We'll be more than happy to accept contributions.

Cheers, everyone!

[Timer]

To summarize the existing changes and the above proposed changes:

v2 Features

1. Babel 7
2. Jest 23
3. webpack 4
4. Babel Macros
5. Compiling node_modules to support packages using newer language features
6. Parallelization of webpack builds to speed up compilation
7. Opt-in support for CSS Modules
8. Opt-in support for Sass
9. Targeted CSS support via browserslist package.json key
10. SVG as React components
11. Remove propTypes definitions in the production build
12. Service workers are now opt-in
13. Long-term webpack caching via consistent hashing and vendor bundles

Features removed from v2

1. Monorepo support (supplanted via documentation)
2. Advanced proxy configuration in package.json (moving to src/setupProxy.js instead)
3. Specifying newer target browsers: all code will be compiled down to ES5 (in line with v1 behavior)
4. mjs extension support

[bjankord]

This list looks good! One ask I have, with "Compiling node_modules to support packages using newer language features", can we get support for dynamic imports in node_modules included in 2.0? CRA supports dynamic imports for "app code". Would like to extend that support for dynamic imports used in dependencies.

#4477

[weyert]

I am curious about the Monorepo support via nwb? I always understood nwb is something similar to create-react-app? Are you talking about a different package? I am interested in this because I would like to do some code sharing between two CRA projects and looking for a good solution to do without publish a package to npm

[gaearon]

The plan (@Timer correct me if I'm wrong) is that we'll support putting CRA in a monorepo but we won't attempt to compile any code outside the project folder (e.g. JSX). You can compile it with tools like nwb though.

[Timer]

re @weyert @gaearon: spot on!
re @bjankord: We have that on our list of considerations. We're not ready to make a final decision.
Unfortunately, the proposal is only stage 3 so we're leaning towards a no.

[SavePointSam]

I've got a working monorepo with a react-scripts@2.0.0-next.3e165448 project inside. I also documented some of the gotchas I encountered along the way. Most of them tended to be that I have to use the same version of certain packages in my other sibling projects due to react-scripts@2's feature of tooling version validation and a bit of yarn's version resolution system.

I'd be happy to share what I've discovered with someone if they wanted to reach out to me. Unfortunately, I don't have the time to directly contribute on documentation at this time, but I do have time for a quick chat and knowledge share.

[tbranyen]

"Parallelization of webpack builds to speed up compilation" What does this mean? That a single build will have webpack tasks spread across the various CPU cores? Or that multiple build configurations will run in parallel?

[Timer]

"Parallelization of webpack builds to speed up compilation" What does this mean? That a single build will have webpack tasks spread across the various CPU cores? Or that multiple build configurations will run in parallel?

That a single build will have webpack tasks spread across the various CPU cores.

---

re @bjankord: Dan and I spoke, we will support dynamic import (import()) in node_modules!

[tbranyen]

@Timer I'm asking ya'll what you mean by that statement. I don't know what it means, and I'm asking for clarification. I proposed some speculations.

[Timer]

Sorry @tbranyen, I didn't mean to leave the question mark -- your speculation was correct. I edited my comment to reflect this.

Processing files through ESLint, Babel, and Minification all happen in worker processes. It'll use all but 1 available cores.

[bjankord]

@Timer @gaearon

You're awesome!