RxJS + babel 7 to reduce bundle size

babel.config.js

const rxjs = {
    Observable: "internal/Observable",
    ConnectableObservable: "internal/observable/ConnectableObservable",
    GroupedObservable: "internal/operators/groupBy",
    observable: "internal/symbol/observable",
    Subject: "internal/Subject",
    BehaviorSubject: "internal/BehaviorSubject",
    ReplaySubject: "internal/ReplaySubject",
    AsyncSubject: "internal/AsyncSubject",
    asapScheduler: "internal/scheduler/asap",
    asyncScheduler: "internal/scheduler/async",
    queueScheduler: "internal/scheduler/queue",
    animationFrameScheduler: "internal/scheduler/animationFrame",
    VirtualTimeScheduler: "internal/scheduler/VirtualTimeScheduler",
    Scheduler: "internal/Scheduler",
    Subscription: "internal/Subscription",
    Subscriber: "internal/Subscriber",
    Notification: "internal/Notification",
    pipe: "internal/util/pipe",
    noop: "internal/util/noop",
    identity: "internal/util/identity",
    isObservable: "internal/util/isObservable",
    ArgumentOutOfRangeError: "internal/util/ArgumentOutOfRangeError",
    EmptyError: "internal/util/EmptyError",
    ObjectUnsubscribedError: "internal/util/ObjectUnsubscribedError",
    UnsubscriptionError: "internal/util/UnsubscriptionError",
    TimeoutError: "internal/util/TimeoutError",
    bindCallback: "internal/observable/bindCallback",
    bindNodeCallback: "internal/observable/bindNodeCallback",
    combineLatest: "internal/observable/combineLatest",
    concat: "internal/observable/concat",
    defer: "internal/observable/defer",
    empty: "internal/observable/empty",
    forkJoin: "internal/observable/forkJoin",
    from: "internal/observable/from",
    fromEvent: "internal/observable/fromEvent",
    fromEventPattern: "internal/observable/fromEventPattern",
    generate: "internal/observable/generate",
    iif: "internal/observable/iif",
    interval: "internal/observable/interval",
    merge: "internal/observable/merge",
    never: "internal/observable/never",
    of: "internal/observable/of",
    onErrorResumeNext: "internal/observable/onErrorResumeNext",
    pairs: "internal/observable/pairs",
    race: "internal/observable/race",
    range: "internal/observable/range",
    throwError: "internal/observable/throwError",
    timer: "internal/observable/timer",
    using: "internal/observable/using",
    zip: "internal/observable/zip",
    EMPTY: "internal/observable/empty",
    NEVER: "internal/observable/never",
    config: "internal/config",
};

const rxjsAjax = {
  ajax: 'internal/observable/dom/ajax',
  AjaxRequest: 'internal/observable/dom/AjaxObservable',
  AjaxResponse: 'internal/observable/dom/AjaxObservable',
  AjaxError: 'internal/observable/dom/AjaxObservable',
  AjaxTimeoutError: 'internal/observable/dom/AjaxObservable',
}

const transformImports = [[
  "transform-imports",
  {
    "rxjs": {
      transform: (importName, matches) => `rxjs/${rxjs[importName]}`,
      "preventFullImport": true,
      "skipDefaultConversion": true
    },
    "rxjs/ajax": {
      transform: (importName, matches) => `rxjs/${rxjsAjax[importName]}`,
      "preventFullImport": true,
      "skipDefaultConversion": true
    },
    "rxjs/operators": {
      "transform": "rxjs/internal/operators/${member}",
      "preventFullImport": true,
      "skipDefaultConversion": true
    },
  }
]];

/// ===================== somewhere where you declare plugins
   plugins: [
       // your plugins
       ...transformImports
   ]
};
// ============================================================