Microbundle: Provide a Jest Transform

[therealparmesh]

It may be convenient to expose something to consumers that will make it easier to use Jest - something like the default babel options (presets, plugins, etc.) or a transform module (see something like https://github.com/ActuallyACat/jest-esm-transformer).

This makes using syntax like import/export much easier for folks who use this amazing library for bundling and Jest for tests.

Thank you!

[developit]

@therealparmesh great suggestion. I see that Jest can already do this when Babel is installed, though because Microbundle abstract Babel Jest likely doesn't detect it. So I guess you're saying it would be nice if there was a Microbundle-provided option here?

If so, I agree!

[therealparmesh]

Precisely what I meant!

FWIW, my current workaround is to have my Jest tests import from dist (You can see it here: https://github.com/therealparmesh/object-to-formdata/blob/b0c0be74a3e510ea8be2efa56f85e4e21ba3afa7/src/index.test.js#L1). This works well - even with features like code coverage (because of the source maps that point to the src).

[therealparmesh]

Any feedback on this? 😄

[hbroer]

microbundle could save the configuration to the project root with a "This is autogenerated. Don't change it."

If microbundle would come with a "public" Babel config, it would also be possible to put a eslint config to the root with just a extend property.

[olance]

If you're ending up here from Google, here's an approach that worked for me:

• Create a babel.config.js file at the project's root:

// Microbundle uses its own Babel config, so we need to make sure we use this only for tests
module.exports =
  process.env.NODE_ENV === 'test'
    ? {
        presets: [
          [
            '@babel/preset-env',
            {
              targets: {
                node: 'current',
              },
            },
            '@babel/preset-react',
          ],
          '@babel/preset-typescript',
        ],
        plugins: [
          [
            '@babel/plugin-transform-runtime',
            {
              regenerator: true,
            },
          ],
          '@babel/plugin-proposal-class-properties',
          '@babel/plugin-proposal-export-default-from',
          ['@babel/plugin-transform-react-jsx', { pragma: 'h' }],
        ],
      }
    : {}

• You'll have to install those plugins/presets with npm install --save-dev (note that I'm using TypeScript; you might want to remove @babel/preset-typescript if you're not)
• Make sure you add NODE_ENV=test to your test scripts, for instance:

    "test": "NODE_ENV=test jest --coverage",
    "test:no-coverage": "NODE_ENV=test jest",
    "test:watch": "NODE_ENV=test jest --coverage --watch",

• If you have a transform option in your Jest configuration, you might need to remove it so that Jest uses the babel-jest transformer.

[marvinhagemeister]

Specifying a babel config for jest is the proper way to do it :+1:

Closing, because shipping microbundle with a jest transform is out of scope for this project. This project's main purpose is to bundle up javascript packages for npm distribution.