yarn start yields a running app, yarn build yields undefined exports variable

[diffent]

per title, yarn start gives a running app. excellent.

but when we try yarn build to make a package for serving, app starts with "whitescreen,"
and in browser console we see:

ReferenceError: Can't find variable: exports

note: this is used in the context of react-native-web build for a browser

i suspect that there is a difference in the build process for development versus production that is somehow
not using some babel setting that is needed, but with the stackup of react-scripts, webpack, babel, babel plugins, babel settings, etc, where this setting is getting lost on the production build is difficult to trace.

it would be good if we could take a "development look-alike" build and make a server build for this, and then gradually put in production efficiency refinements rather than jumping directly from full devel to full production.

[diffent]

FYI we partly solved the issue:

in node_modules/react-scripts/scripts/build.js :

near the top of the file, change both of these variables to 'development' , viz:

// Do this as the first thing so that any code reading it knows the right env.
process.env.BABEL_ENV = 'development';
process.env.NODE_ENV = 'development';

in node_modules/react-scripts/config/webpack.config.js :

find where the isEnv* variables are set up, and set the isEnv* variables to the proper boolean values to force development mode:

module.exports = function(webpackEnv) {
const isEnvDevelopment = true // webpackEnv === 'development';
const isEnvProduction = false // webpackEnv === 'production';

then a yarn build makes a dist folder that seems to run ok in browser without
the undefined exports variable problem. (the build folder is empty for some reason,
but it doesnt seem to matter, the build ends up in a folder named dist). the build may
not (will not) be optimized, compressed, obfuscated, etc. which is fine for our project
now, we can optimize later.

note that the two files build.js and webpack.config.js get overwritten upon yarn install, so you may have
to do the eject thing which we havent tried yet and edit them, or put the edited version of those 2 files in
a safe place e.g. root of the project, and copy them to where they belong under node_modules/react-scripts/* before a build, or fork react-scripts and edit the fork and
put the fork link in your main package.json for react-scripts, etc. there may be more ways to override these configs which react-scripts / webpack experts will know better about.