Why differences in babel config for test env?

[justin808]

Regarding the example babel config files:

Is this necessary:
https://github.com/rails/webpacker/blob/master/lib/install/examples/react/babel.config.js#L26

and why the setting of targets.node='current' for test env only?

This is definitely related: #416

But I think it's not necessary with newer versions of babel, jest, node, etc.

And simpler is better, generally.

return {
    presets: [
      isTestEnv && [
        '@babel/preset-env',
        {
          targets: {
            node: 'current'
          }
        }
      ],
      (isProductionEnv || isDevelopmentEnv) && [
        '@babel/preset-env',
        {
          forceAllTransforms: true,
          useBuiltIns: 'entry',
          corejs: 3,
          modules: false,
          exclude: ['transform-typeof-symbol']
        }
      ]

I think just adding this plugin for the test env would do the trick:

      plugins.push('@babel/plugin-transform-modules-commonjs');

[jakeNiemiec]

why the setting of targets.node='current' for test env only?

Users may not be running the current release of node. Some temperamental libraries don't yet support new things in current since it's the bleeding edge.

Is this necessary: modules: 'commonjs'

I think so for the following reasons:

• If not set, I think it defaults to ES modules from webpack (or so I have read). These are not supported in all versions of nodejs (which jest uses to run).
• Depending on the version, you need to additionally include the --experimental-modules flag

I don't think we will need to worry about this for very long since [email protected] has removed the flag requirement.

[justin808]

This issue was well explained by @rossta: Why doesn't Webpacker use my test config when I run Rails tests?
.

In summary, NODE_ENV == 'test' is used to run JS unit tests.