.babelrc.js

const importTransforms = {
  'rxjs/operators': {
    transform: 'rxjs/_esm5/internal/operators/${member}',
    preventFullImport: true,
    skipDefaultConversion: true,
  },
  'rxjs/observable': {
    transform: 'rxjs/_esm5/internal/observable/${member}',
    preventFullImport: true,
    skipDefaultConversion: true,
  },
  'rxjs': {
    transform: 'rxjs/_esm5/internal/${member}',
    preventFullImport: true,
    skipDefaultConversion: true,
  },
}

module.exports = function (api) {
  api.cache(true)

  const presets = [
    ['@babel/preset-env', { modules: false }],
  ]
  const plugins = [
    // Stage 0
    '@babel/plugin-proposal-function-bind',
    // Stage 1
    '@babel/plugin-proposal-export-default-from',
    '@babel/plugin-proposal-logical-assignment-operators',
    ['@babel/plugin-proposal-optional-chaining', { loose: false }],
    ['@babel/plugin-proposal-pipeline-operator', { proposal: 'minimal' }],
    ['@babel/plugin-proposal-nullish-coalescing-operator', { loose: false }],
    '@babel/plugin-proposal-do-expressions',
    // Stage 2
    ['@babel/plugin-proposal-decorators', { legacy: true }],
    '@babel/plugin-proposal-function-sent',
    '@babel/plugin-proposal-export-namespace-from',
    '@babel/plugin-proposal-numeric-separator',
    '@babel/plugin-proposal-throw-expressions',
    // Stage 3
    '@babel/plugin-syntax-dynamic-import',
    '@babel/plugin-syntax-import-meta',
    ['@babel/plugin-proposal-class-properties', { loose: false }],
    '@babel/plugin-proposal-json-strings',
    // Other
    ['@babel/plugin-transform-runtime', { corejs: 2, helpers: true, regenerator: true, useESModules: true }],
    ['transform-imports', importTransforms],
  ]
  const env = {
    test: {
      plugins: [
        'istanbul',
      ],
    },
  }

  return {
    presets,
    plugins,
    env,
  }
}