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**Subdirectory plugins** (e.g. `plugin/` in a monorepo):

The action's install step runs at the repo root and cannot find `yarn.lock` in a subdirectory. Work around this by installing deps yourself and symlinking to root:

```yaml
jobs:
  bundle-size:
    runs-on: ubuntu-latest
    permissions:
      contents: write
      id-token: write
      pull-requests: write
      actions: read
    steps:
      - uses: actions/checkout@v4
      - uses: actions/setup-node@v4
        with:
          node-version-file: ./plugin/.nvmrc
      - name: Install dependencies
        working-directory: ./plugin
        run: yarn install
      - name: Symlink plugin to root for bundle-size action
        run: |
          ln -s plugin/yarn.lock yarn.lock
          ln -s plugin/package.json package.json
          ln -s plugin/.yarnrc.yml .yarnrc.yml
          ln -s plugin/node_modules node_modules
      - name: Bundle Size
        uses: grafana/plugin-actions/bundle-size@a66a1c96cdbb176f9cccf10cf23593e250db7cce # bundle-size/v1.1.0
        with:
          working-directory: ./plugin

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Record the baseline. A pre-split plugin commonly has a `module.js` of 1–3 MB with no other JS chunks.

---

cat .config/.cprc.json 2>/dev/null || grep '"@grafana/create-plugin"' package.json
npm view @grafana/create-plugin version
npx @grafana/create-plugin@latest update

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**Key rule:** If a file is imported by `module.ts` directly (even transitively), it ends up in `module.js`. Everything reachable from a lazy boundary becomes its own chunk.

---

import React, { lazy, Suspense } from 'react';
import { AppPlugin, AppRootProps } from '@grafana/data';
import { LoadingPlaceholder } from '@grafana/ui';

import type { MyExtensionProps } from './extensions/MyExtension';  // import type — erased at compile time
import type { JsonData } from './features/app/state/slice';

// Lazy Faro init — keeps @grafana/faro-react out of module.js
let faroInitialized = false;
async function initFaro() {
  if (faroInitialized) { return; }
  faroInitialized = true;
  const { initializeFaro } = await import('faro');
  initializeFaro();
}

const LazyApp = lazy(async () => {
  await initFaro();
  return import('./features/app/App').then(m => ({ default: m.App }));
});

function App(props: AppRootProps<JsonData>) {
  return <Suspense fallback={<LoadingPlaceholder text="" />}><LazyApp {...props} /></Suspense>;
}

const LazyMyExtension = lazy(() =>
  import('./extensions/MyExtension').then(m => ({ default: m.MyExtension }))
);
function MyExtension(props: MyExtensionProps) {
  return <Suspense fallback={<LoadingPlaceholder text="" />}><LazyMyExtension {...props} /></Suspense>;
}

export const plugin = new AppPlugin<JsonData>().setRootPage(App);
plugin.exposeComponent({ id: 'my-plugin/my-extension/v1', title: 'My Extension', component: MyExtension });

import React, { lazy, Suspense } from 'react';
import { Route, Routes } from 'react-router-dom';
import { LoadingPlaceholder } from '@grafana/ui';

const HomePage     = lazy(() => import('../pages/Home'));
const SettingsPage = lazy(() => import('../pages/Settings'));
const DetailPage   = lazy(() => import('../pages/Detail'));

function App(props: AppRootProps) {
  return (
    <Suspense fallback={<LoadingPlaceholder text="" />}>
      <Routes>
        <Route path="home"       element={<HomePage />} />
        <Route path="settings"   element={<SettingsPage />} />
        <Route path="detail/:id" element={<DetailPage />} />
        <Route path=""           element={<HomePage />} />
      </Routes>
    </Suspense>
  );
}
export default App;

// Risky — barrel may pull in other heavy modules
const Catalog = lazy(() => import('features/catalog'));
// Better — only pulls in Catalog's tree
const Catalog = lazy(() => import('features/catalog/Catalog').then(m => ({ default: m.Catalog })));

// src/extensions/MyExtension.tsx
export default function MyExtension(props: MyExtensionProps) {
  return <AppProviders><MyExtensionContent {...props} /></AppProviders>;
}

const HeavyInner = lazy(() => import('components/features/HeavyInner'));
export function MyExtension() {
  return <Suspense fallback={<LoadingPlaceholder text="" />}><HeavyInner /></Suspense>;
}

const ConfigDetails = lazy(() => import('./ConfigDetails/ConfigDetails').then(m => ({ default: m.ConfigDetails })));
const Overview      = lazy(() => import('./Overview/Overview').then(m => ({ default: m.Overview })));

const tabs = [
  { id: 'overview', component: Overview },
  { id: 'config',   component: ConfigDetails },
];

// In the parent that renders the active tab:
<Suspense fallback={<LoadingPlaceholder text="" />}>
  {ActiveTab && <ActiveTab />}
</Suspense>

const FleetList   = lazy(() => import(/* webpackChunkName: "fleet" */ '../pages/FleetList'));
const FleetDetail = lazy(() => import(/* webpackChunkName: "fleet" */ '../pages/FleetDetail'));

yarn build 2>/dev/null || npm run build
echo "=== module.js ===" && ls -lah dist/module.js
echo "=== all JS chunks (largest first) ===" && ls -lah dist/*.js | sort -k5 -rh | head -30
echo "=== chunk count ===" && ls dist/*.js | wc -l

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---