Merge pull request #60 from storybookjs/peer-dependency-bundling

Smarter bundling strategy

README.md

@@ -70,6 +70,32 @@ Your addon might use one or more of these patterns. Feel free to delete unused c
 
 Lastly, configure you addon name in `src/constants.ts`.
 
+### Bundling
+
+Addons can interact with a Storybook project in multiple ways. It is recommended to familiarize yourself with [the basics](https://storybook.js.org/docs/react/addons/introduction) before getting started.
+
+- Manager entries are used to add UI or behavior to the Storybook manager UI.
+- Preview entries are used to add UI or behavior to the preview iframe where stories are rendered.
+- Presets are used to modify the Storybook configuration, similar to how [users can configure their `main.ts` configurations](https://storybook.js.org/docs/react/api/main-config).
+
+Since each of these places represents a different environment with different features and modules, it is also recommended to split and build your modules accordingly. This addon-kit comes with a preconfigured [bundling configuration](./tsup.config.ts) that supports this split, and you are free to modify and extend it as needed.
+
+You can define which modules match which environments in the [`package.json#bundler`](./package.json) property:
+
+- `exportEntries` is a list of module entries that users can manually import from anywhere they need to. For example, you could have decorators that users need to import into their `preview.ts` file or utility functions that can be used in their `main.ts` files.
+- `managerEntries` is a list of module entries meant only for the manager UI. These modules will be bundled to ESM and won't include types since they are mostly loaded by Storybook directly.
+- `previewEntries` is a list of module entries meant only for the preview UI. These modules will be bundled to ESM and won't include types since they are mostly loaded by Storybook directly.
+
+Manager and preview entries are only used in the browser so they only output ESM modules. Export entries could be used both in the browser and in Node depending on their use case, so they both output ESM and CJS modules.
+
+#### Globalized packages
+
+Storybook provides a predefined set of packages that are available in the manager UI and the preview UI. In the final bundle of your addon, these packages should not be included. Instead, the imports should stay in place, allowing Storybook to replace those imports with the actual packages during the Storybook build process.
+
+The list of packages differs between the manager and the preview, which is why there is a slight difference between `managerEntries` and `previewEntries`. Most notably, `react` and `react-dom` are prebundled in the manager but not in the preview. This means that your manager entries can use React to build UI without bundling it or having a direct reference to it. Therefore, it is safe to have React as a `devDependency` even though you are using it in production. _Requiring React as a peer dependency would unnecessarily force your users to install React._
+
+An exception to this rule is if you are using React to inject UI into the preview, which does not come prebundled with React. In such cases, you need to move `react` and `react-dom` to a peer dependency. However, we generally advise against this pattern since it would limit the usage of your addon to React-based Storybooks.
+
 ### Metadata
 
 Storybook addons are listed in the [catalog](https://storybook.js.org/addons) and distributed via npm. The catalog is populated by querying npm's registry for Storybook-specific metadata in `package.json`. This project has been configured with sample data. Learn more about available options in the [Addon metadata docs](https://storybook.js.org/docs/react/addons/addon-catalog#addon-metadata).