Make it easier to properly profile with the React DevTools.

[kentcdodds]

I wrote a blog post about how to properly profile a React App for Performance and I use a react-scripts app to demonstrate how to do it. There are a few steps in there that I'd love to make easier.

Specifically, you have to go into ./node_modules/react-scripts/config/webpack.config.js to update the webpack config to add this to resolve.alias:

'react-dom$': 'react-dom/profiling',
'scheduler/tracing': 'scheduler/tracing-profiling',

And you have to add this to the Terser options:

keep_classnames: true,
keep_fnames: true,

It's a bit of an annoying process and I think we could make it a lot easier (and hopefully encourage people to profile their apps in the process).

Describe the solution you'd like

We'd make a change here:

create-react-app/packages/react-scripts/config/webpack.config.js

Lines 302 to 306 in 0d1775e

	alias: {
	// Support React Native Web
	// https://www.smashingmagazine.com/2016/08/a-glimpse-into-the-future-with-react-native-for-web/
	'react-native': 'react-native-web',
	},

-      alias: {
+      alias: removeEmpty({
         // Support React Native Web
         // https://www.smashingmagazine.com/2016/08/a-glimpse-into-the-future-with-react-native-for-web/
         'react-native': 'react-native-web',
+        'react-dom$': isEnvProductionProfile ? 'react-dom/profiling' : null,
+        'scheduler/tracing': isEnvProductionProfile ? 'scheduler/tracing-profiling' : null,
+      }),
-      },

Where removeEmpty is something like (borrowed from webpack-config-utils):

function removeEmpty(input) {
  const output = {}
  Object.keys(input).forEach(key => {
    const value = input[key]
    if (typeof value !== 'undefined') {
      output[key] = value
    }
  })
  return output
}

and isEnvProductionProfile is defined as: isEnvProduction && Boolean(process.env.PROFILE_APP).

We'd also add this right above:

create-react-app/packages/react-scripts/config/webpack.config.js

Line 237 in 0d1775e

output: {

keep_classnames: isEnvProductionProfile,
keep_fnames: isEnvProductionProfile,

Describe alternatives you've considered

Currently the alternative is to change it manually (and if you deploy from your local build then you need to remember to remove your edits).

Additional context

I'm bringing this up because I'd love to update my blog post to simply be: "Now, run the build in profiling mode with npx cross-env PROFILE_APP=true npm run build." That would be awesome. And it would make every-day profiling much simpler as well.

[kentcdodds]

By the way, I don't really care exactly how this is implemented. If you don't like the environment variable/removeEmpty function/etc, that's fine. I just want to make this easier.

[JacobMGEvans]

Are those steps to implementing this? Could we just make a PR then?

[kentcdodds]

I think so!

[jamesb3ll]

Instead of removeEmpty function, spread operator could be used:

alias: {
  'react-native': 'react-native-web',
  ...(isEnvProductionProfile && {
    'react-dom$': 'react-dom/profiling',
    'scheduler/tracing': 'scheduler/tracing-profiling',
  }),
}

[JacobMGEvans]

Instead of removeEmpty function, spread operator could be used:

alias: {
  'react-native': 'react-native-web',
  ...(isEnvProductionProfile && {
    'react-dom$': 'react-dom/profiling',
    'scheduler/tracing': 'scheduler/tracing-profiling',
  }),
}

Would any type safety be lost? Or would that short circuit be handling that logically equivalent?

[JacobMGEvans]

I started to implement this here is the draft PR: #7737
Currently, I have an issue with the keep_classnames and I am guessing keep_fnames might have some issues.
Here is the current compiler error:
yarn run v1.17.3
$ cd packages/react-scripts && node bin/react-scripts.js build
Creating an optimized production build...
Failed to compile.

Failed to minify the bundle. Error: static/js/main.b21b40a1.chunk.js from Terser
`keep_classnames` is not a supported option
    at /Users/jacobevans/personalProjects/create-react-app/packages/react-scripts/scripts/build.js:176:23
    at finalCallback (/Users/jacobevans/personalProjects/create-react-app/node_modules/webpack/lib/Compiler.js:257:39)
    at /Users/jacobevans/personalProjects/create-react-app/node_modules/webpack/lib/Compiler.js:273:13
    at AsyncSeriesHook.eval [as callAsync] (eval at create (/Users/jacobevans/personalProjects/create-react-app/node_modules/tapable/lib/HookCodeFactory.js:33:10), <anonymous>:6:1)
    at AsyncSeriesHook.lazyCompileHook (/Users/jacobevans/personalProjects/create-react-app/node_modules/tapable/lib/Hook.js:154:20)
    at onCompiled (/Users/jacobevans/personalProjects/create-react-app/node_modules/webpack/lib/Compiler.js:271:21)
    at /Users/jacobevans/personalProjects/create-react-app/node_modules/webpack/lib/Compiler.js:681:15
    at AsyncSeriesHook.eval [as callAsync] (eval at create (/Users/jacobevans/personalProjects/create-react-app/node_modules/tapable/lib/HookCodeFactory.js:33:10), <anonymous>:6:1)
    at AsyncSeriesHook.lazyCompileHook (/Users/jacobevans/personalProjects/create-react-app/node_modules/tapable/lib/Hook.js:154:20)
    at /Users/jacobevans/personalProjects/create-react-app/node_modules/webpack/lib/Compiler.js:678:31
    at AsyncSeriesHook.eval [as callAsync] (eval at create (/Users/jacobevans/personalProjects/create-react-app/node_modules/tapable/lib/HookCodeFactory.js:33:10), <anonymous>:6:1)
    at AsyncSeriesHook.lazyCompileHook (/Users/jacobevans/personalProjects/create-react-app/node_modules/tapable/lib/Hook.js:154:20)
    at /Users/jacobevans/personalProjects/create-react-app/node_modules/webpack/lib/Compilation.js:1423:35
    at AsyncSeriesHook.eval [as callAsync] (eval at create (/Users/jacobevans/personalProjects/create-react-app/node_modules/tapable/lib/HookCodeFactory.js:33:10), <anonymous>:6:1)
    at AsyncSeriesHook.lazyCompileHook (/Users/jacobevans/personalProjects/create-react-app/node_modules/tapable/lib/Hook.js:154:20)
    at /Users/jacobevans/personalProjects/create-react-app/node_modules/webpack/lib/Compilation.js:1414:32
Read more here: https://bit.ly/CRA-build-minify

[kevin940726]

@JacobMGEvans I left the comment in the PR :)

[JacobMGEvans]

@kevin940726 Pointing out I had the keep_classnames and keep_fnames inside of the
output: { ... } rather than outside of it in the scope of the terserOptions: { ... }

@kentcdodds works as you expected now, I just misread your direction for that part of the implementation.

[kentcdodds]

Huzzah!!!! Thanks @iansu! And well done @JacobMGEvans 👏

I understand that my needs are not your deadlines, but if this could be released for my workshop by next Monday that would be awesome 😁

[iansu]

@kentcdodds It's released now!