babel.config.js

'use strict';
// * Every now and then, we adopt best practices from CRA
// * https://tinyurl.com/yakv4ggx

// ? https://nodejs.org/en/about/releases
const NODE_LTS = 'maintained node versions';
// TODO: replace with 'package'
const pkgName = require('./package.json').name;
const debug = require('debug')(`${pkgName}:babel-config`);

debug('NODE_ENV: %O', process.env.NODE_ENV);

/**
 * @type {import('@babel/core').TransformOptions}
 */
module.exports = {
  comments: false,
  parserOpts: { strictMode: true },
  assumptions: {
    constantReexports: true
  },
  plugins: [
    '@babel/plugin-proposal-export-default-from',
    [
      'module-resolver',
      {
        root: '.',
        extensions: ['.ts', '.tsx', '.js', '.jsx', '.json'],
        // ! If changed, also update these aliases in tsconfig.json,
        // ! webpack.config.js, next.config.ts, eslintrc.js, and jest.config.js
        alias: {
          '^universe/(.*)$': String.raw`./src/\1`,
          '^multiverse/(.*)$': String.raw`./lib/\1`,
          '^testverse/(.*)$': String.raw`./test/\1`,
          '^externals/(.*)$': String.raw`./external-scripts/\1`,
          '^types/(.*)$': String.raw`./types/\1`,
          '^package$': `./package.json`
        }
      }
    ]
  ],
  // ? Sub-keys under the "env" config key will augment the above
  // ? configuration depending on the value of NODE_ENV and friends. Default
  // ? is: development
  env: {
    // * Used by Jest and `npm test`
    test: {
      comments: true,
      sourceMaps: 'inline',
      presets: [
        ['@babel/preset-env', { targets: { node: true } }],
        ['@babel/preset-typescript', { allowDeclareFields: true }]
        // ? We don't care about minification
      ],
      plugins: [
        // ? Only active when testing, the plugin solves the following problem:
        // ? https://stackoverflow.com/q/40771520/1367414
        'explicit-exports-references'
      ]
    },
    // * Used when NODE_ENV === production (usually for generating types w/ tsc)
    production: {
      presets: [
        [
          '@babel/preset-env',
          {
            // ? https://babeljs.io/docs/en/babel-preset-env#modules
            modules: 'auto',
            targets: NODE_LTS,
            exclude: ['proposal-dynamic-import']
          }
        ],
        ['@babel/preset-typescript', { allowDeclareFields: true }]
        // ? Minification is handled externally (e.g. by webpack)
      ]
    },
    // * Used by `npm run build` for transpiling TS to CJS output in ./dist
    'production-cjs': {
      presets: [
        [
          '@babel/preset-env',
          {
            // ? https://babeljs.io/docs/en/babel-preset-env#modules
            modules: 'cjs',
            targets: NODE_LTS,
            useBuiltIns: 'usage',
            corejs: '3.37',
            shippedProposals: true,
            exclude: ['proposal-dynamic-import']
          }
        ],
        ['@babel/preset-typescript', { allowDeclareFields: true }]
      ],
      plugins: [
        [
          'transform-rewrite-imports',
          {
            replaceExtensions: {
              '^../package.json$': '../../package.json'
            }
          }
        ]
      ]
    },
    // * Used by `npm run build:externals` for compiling to ESM code output in
    // * ./external-scripts/bin
    'production-external': {
      presets: [
        [
          '@babel/preset-env',
          {
            // ? https://babeljs.io/docs/en/babel-preset-env#modules
            modules: 'cjs',
            targets: NODE_LTS,
            useBuiltIns: 'usage',
            corejs: '3.36',
            shippedProposals: true,
            exclude: ['proposal-dynamic-import']
          }
        ],
        ['@babel/preset-typescript', { allowDeclareFields: true }]
      ],
      plugins: [
        [
          'transform-rewrite-imports',
          {
            replaceExtensions: {
              '^../package.json$': '../../package.json',
              '^../test/util$': './util.js'
            }
          }
        ]
      ]
    }
  }
};

debug('exports: %O', module.exports);