1# Expo Module Scripts
2
3This package contains a collection of common scripts for all Expo modules and the Expo SDK package. This sets us up to have a consistent way of compiling JS, testing, linting, and other common tasks so that the Expo SDK is coherent and unified. Knowledge and experience from working on an Expo module in this repository will carry over to working on other modules. And ultimately, we want the development experience for Expo developers to be similar across modules. A structurally unified way of developing Expo modules helps us achieve these goals.
4
5**This is the package that installs Babel CLI, TypeScript, Jest, and other common development dependencies.** Update the dependencies in this package when changing them for the Expo repository.
6
7- [Getting Started](#getting-started)
8- [Setup](#setup)
9  - [�� Config Plugin](#-config-plugin)
10  - [�� Jest](#-jest)
11  - [�� LICENSE](#-license)
12  - [Side Effects](#side-effects)
13  - [Entry Point and Types](#entry-point-and-types)
14  - [�� npm Linking](#-npm-linking)
15- [⌘ Commands](#-commands)
16  - [configure](#configure)
17  - [typecheck](#typecheck)
18  - [build](#build)
19  - [test](#test)
20  - [lint](#lint)
21  - [clean](#clean)
22- [Lifecycle Commands](#lifecycle-commands)
23  - [prepare (npm lifecycle)](#prepare--npm-lifecycle-)
24  - [prepublishOnly (npm lifecycle)](#prepublishonly--npm-lifecycle-)
25- [Excluding Files from npm](#excluding-files-from-npm)
26- [Unified Dependencies](#unified-dependencies)
27
28## Getting Started
29
30```sh
31yarn add -D expo-module-scripts
32
33# or
34
35npm install --save-dev expo-module-scripts
36```
37
38## Setup
39
40Add the following scripts to your `package.json` and run `yarn`
41
42```json
43{
44  "scripts": {
45    "build": "expo-module build",
46    "clean": "expo-module clean",
47    "test": "expo-module test",
48    "prepare": "expo-module prepare",
49    "prepublishOnly": "expo-module prepublishOnly",
50    "expo-module": "expo-module"
51  }
52}
53```
54
55Running `yarn` will now run the `prepare` script, which generates any missing files:
56
57- [`.eslintrc.js`](./templates/.eslintrc.js) ([docs](https://eslint.org/docs/user-guide/configuring)) this extends [`eslint-config-universe`](https://github.com/expo/expo/tree/main/packages/eslint-config-universe).
58  - Optionally you can customize Prettier too: [.prettierrc guide](https://github.com/expo/expo/tree/main/packages/eslint-config-universe#customizing-prettier).
59- [`.npmignore`](./templates/.npmignore) ([docs](https://docs.npmjs.com/misc/developers)) currently only ignores the `babel.config.js` in your module. You might also want to also add tests and docs.
60  - Expo modules use `.npmignore` **instead of** the `files` field in the `package.json`.
61  - (Pro Tip) Test which files get packaged by running `npm pack`. If you see files that aren't crucial to running the module, you should add them to `.npmignore`.
62- [`README.md`](./templates/README.md) A default template for Unimodule installation.
63  - Project docs should try to have relevant emojis in headers because OSS is fun.
64  - Use [badges](https://github.com/expo/expo#-badges)
65  - Try and incorporate a table of contents (TOC).
66- [`tsconfig.json`](./templates/tsconfig.json) ([docs](https://www.typescriptlang.org/docs/handbook/tsconfig-json.html)) extends [`tsconfig.base.json`](./tsconfig.base.json) this is important for ensuring all Unimodules use the same version of TypeScript.
67
68Besides, running `yarn prepare` script will also synchronize optional files from `expo-module-scripts` when the file is present and contains the `@generated` pattern:
69
70- [`with-node.sh`](./templates/scripts/with-node.sh): An Xcode build phase script helper for Node.js binary resolution. It sources the project's **.xcode.env** and **.xcode.env.local** files, which may define an environment variable named `NODE_BINARY` to specify the file path of the Node.js binary to run.
71
72### �� Config Plugin
73
74To create a [config plugin](https://github.com/expo/expo/blob/main/packages/@expo/config-plugins/README.md) that automatically configures your native code, you have two options:
75
761. Create a `plugin` folder and write your plugin in TypeScript (recommended).
772. Create an `app.plugin.js` file in the project root and write the plugin in pure Node.js-compliant JavaScript.
78
79Config plugins must be transpiled for compatibility with Node.js (LTS). The features supported in Node.js are slightly different from those in Expo or React Native modules, which support ES6 import/export keywords and JSX, for example. This means we'll need two different `tsconfig.json` files and two different `src` (and `build`) folders — one for the code that will execute in an Expo or React Native app and the other for the plugin that executes in Node.js.
80
81This can quickly become complex, so we've created a system for easily targeting the plugin folder.
82
83#### Plugin setup
84
85The following files are required for a TypeScript plugin:
86
87```
88╭── app.plugin.js ➡️ Entry file
89╰── plugin/ ➡️ All code related to the plugin
90    ├── __tests__/ ➡️ Optional: Folder for tests related to the plugin
91    ├── tsconfig.json ➡️ The TypeScript config for transpiling the plugin to JavaScript
92    ├── jest.config.js ➡️ Optional: The Jest preset
93    ╰── src/index.ts ➡️ The TypeScript entry point for your plugin
94```
95
96Create an `app.plugin.js` (the entry point for a config plugin):
97
98```js
99module.exports = require('./plugin/build');
100```
101
102Create a `plugin/tsconfig.json` file. Notice that this uses `tsconfig.plugin` as the base config:
103
104```json
105{
106  "extends": "expo-module-scripts/tsconfig.plugin",
107  "compilerOptions": {
108    "outDir": "build",
109    "rootDir": "src"
110  },
111  "include": ["./src"],
112  "exclude": ["**/__mocks__/*", "**/__tests__/*"]
113}
114```
115
116In your `plugin/src/index.ts` file, write your TypeScript config plugin:
117
118```ts
119import { ConfigPlugin } from '@expo/config-plugins';
120
121const withNewName: ConfigPlugin<{ name?: string }> = (config, { name = 'my-app' } = {}) => {
122  config.name = name;
123  return config;
124};
125
126export default withNewName;
127```
128
129> �� Tip: Using named functions makes debugging easier with `EXPO_DEBUG=true`
130
131Optionally, you can add `plugin/jest.config.js` to override the default project Jest preset.
132
133```ts
134module.exports = require('expo-module-scripts/jest-preset-plugin');
135```
136
137Use the following scripts to interact with the plugin:
138
139- `yarn build plugin`: Build the plugin.
140- `yarn clean plugin`: Delete the `plugin/build` folder.
141- `yarn lint plugin`: Lint the `plugin/src` folder.
142- `yarn test plugin`: Alias for `npx jest --rootDir ./plugin --config ./plugin/jest.config.js`, uses the project's Jest preset if `plugin/jest.config.js` doesn't exist.
143- `yarn prepare`: Prepare the plugin and module for publishing.
144
145### �� Jest
146
147The Jest preset extends [`jest-expo`](https://github.com/expo/expo/tree/main/packages/jest-expo) and adds proper TypeScript support and type declarations to the presets.
148
149**For unit testing API-based modules:**
150
151```json
152{
153  "jest": {
154    "preset": "expo-module-scripts"
155  }
156}
157```
158
159**For unit testing component-based modules** use @testing-library/react and @testing-library/react-native.
160
161### �� LICENSE
162
163This makes it easier for other members of the community to work with your package. Expo usually has the **MIT** license.
164
165```json
166{
167  "license": "MIT"
168}
169```
170
171### Side Effects
172
173The [`@expo/webpack-config`](https://www.npmjs.com/package/@expo/webpack-config) is optimized for tree-shaking, you should always make sure to list whatever files in your module have side effects. In Expo modules we use the `.fx.*` extension on these files (this makes it easier to target them with `sideEffects`).
174
175[**Learn more about side effects**](https://webpack.js.org/guides/tree-shaking/)
176
177```json
178{
179  "sideEffects": false
180}
181```
182
183### Entry Point and Types
184
185We recommend you name the initial file after the module for easier searching. Be sure to define the `types` file as well.
186
187> �� Note that the `"typings"` field is synonymous with `"types"` field, Expo uses the TypeScript preferred `"types"` field.
188
189[**Learn more about "types" field**](https://webpack.js.org/guides/tree-shaking/)
190
191```json
192{
193  "main": "build/Camera.js",
194  "types": "build/Camera.d.ts"
195}
196```
197
198> �� You technically don't need to define the types file if it's named the same as the `main` file but Expo modules always define it (which is what TypeScript recommends).
199
200### �� npm Linking
201
202Make your package accessible to npm users by adding the following fields:
203
204Expo modules use the long form object when possible to better accommodate monorepos and hyperlinks:
205
206- [homepage docs](https://docs.npmjs.com/files/package.json#homepage)
207- [bugs docs](https://docs.npmjs.com/files/package.json#bugs)
208- [repository docs](https://docs.npmjs.com/files/package.json#repository)
209
210```json
211{
212  "homepage": "https://github.com/YOU/expo-YOUR_PACKAGE#readme",
213  "repository": {
214    "type": "git",
215    "url": "git+https://github.com/YOU/expo-YOUR_PACKAGE.git"
216  },
217  "bugs": {
218    "url": "https://github.com/YOU/expo-YOUR_PACKAGE/issues"
219  }
220}
221```
222
223## ⌘ Commands
224
225This package defines a program called `expo-module` that accepts a command (ex: `expo-module build`). This allows us to add more commands without changing the behavior of existing commands while not needing to define more programs. Typically, you'd invoke these commands from Yarn:
226
227```sh
228$ cd expo-example-module
229$ yarn expo-module test
230
231# For commonly run commands, add "expo-module test" as an npm script named "test"
232$ yarn test
233```
234
235For scripts that need to run as part of the npm lifecycle, you'd invoke the commands from npm scripts in package.json:
236
237```json
238{
239  "scripts": {
240    "prepare": "expo-module prepare",
241    "prepublishOnly": "expo-module prepublishOnly"
242  }
243}
244```
245
246These are the commands:
247
248### configure
249
250This generates common configuration files like `tsconfig.json` for the package. These auto-generated files are meant to be read-only and committed to Git.
251
252### typecheck
253
254This type checks the source TypeScript with `tsc`. This command is separate from `build` and does not emit compiled JS.
255
256### build
257
258This compiles the source JS or TypeScript to "compiled" JS that Expo can load. We use `tsc` instead of the Babel TypeScript plugin since `tsc` has complete support for the TypeScript language, while the Babel plugin has [some limitations](https://blogs.msdn.microsoft.com/typescript/2018/08/27/typescript-and-babel-7/). `tsc` also performs type checking in the same way that VS Code and other IDEs do.
259
260If we wished to switch to using just Babel with the TypeScript plugin, this package would let us change the implementation of the `build` command and apply it to all packages automatically.
261
262#### build plugin
263
264Running `build plugin` builds the plugin source code in `plugin/src`.
265
266### test
267
268We run tests using Jest with ts-jest, which runs TypeScript and Babel. This setup type checks test files and mimics the `build` command's approach of running `tsc` followed by Babel.
269
270If we were to use just Babel with the TypeScript plugin for the `build` command, Jest with `babel-jest` would be more closely aligned.
271
272### lint
273
274This runs ESLint over the source JS and TypeScript files.
275
276One of the rules enforced is restricting any imports from the `fbjs` library. As stated in that [library's readme](https://github.com/facebook/fbjs#purpose):
277
278> If you are consuming the code here and you are not also a Facebook project, be prepared for a bad time.
279
280Replacements for common `fbjs` uses-cases are listed below:
281
282- `invariant`- replace with [`invariant`](https://www.npmjs.com/package/invariant)
283- `ExecutionEnvironment`- replace with [`Platform` from `@unimodules/core`](https://github.com/expo/expo/blob/main/packages/%40unimodules/react-native-adapter/src/Platform.ts)
284
285#### lint plugin
286
287Running `lint plugin` will lints the plugin source code in `plugin/src`.
288
289### clean
290
291This deletes the build directory.
292
293#### clean plugin
294
295Running `clean plugin` will delete the `plugin/build` directory.
296
297## Lifecycle Commands
298
299These are commands to run as part of [the npm scripts lifecycle](https://docs.npmjs.com/misc/scripts).
300
301### prepare (npm lifecycle)
302
303Runs `clean` and `build`.
304
305### prepublishOnly (npm lifecycle)
306
307Runs `npm-proofread`, which ensures a [dist-tag](https://docs.npmjs.com/cli/dist-tag) is specified when publishing a prerelease version.
308
309## Excluding Files from npm
310
311By convention, `expo-module-scripts` uses `.npmignore` to exclude all top-level hidden directories (directories starting with `.`) from being published to npm. This behavior is useful for files that need to be in the Git repository but not in the npm package.
312
313## Unified Dependencies
314
315This package depends on common development dependencies like Babel and Jest. The commands for compiling and testing JS need these dependencies, and the most important benefit is that all Expo module packages use the same version of Babel, Jest, their various plugins, and other development dependencies. This does remove the flexibility to customize the dependency versions for each module. We intentionally make this tradeoff to prioritize Expo as a whole over individual modules.
316