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/master/packages/eslint-config-universe).
58  - Optionally you can customize Prettier too: [.prettierrc guide](https://github.com/expo/expo/tree/master/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
68You should also add the following fields to your `package.json`:
69
70### �� Config Plugin
71
72To create a [config plugin](https://github.com/expo/expo-cli/blob/master/packages/config-plugins/README.md) that automatically configures your native code, you have two options:
73
741. Create a `plugin` folder and write your plugin in TypeScript (recommended).
752. Create an `app.plugin.js` file in the project root and write the plugin in pure Node.js-compliant JavaScript.
76
77Config 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.
78
79This can quickly become complex, so we've created a system for easily targeting the plugin folder.
80
81#### Plugin setup
82
83The following files are required for a TypeScript plugin:
84
85```
86╭── app.plugin.js ➡️ Entry file
87╰── plugin/ ➡️ All code related to the plugin
88    ├── __tests__/ ➡️ Optional: Folder for tests related to the plugin
89    ├── tsconfig.json ➡️ The TypeScript config for transpiling the plugin to JavaScript
90    ├── jest.config.js ➡️ Optional: The Jest preset
91    ╰── src/index.ts ➡️ The TypeScript entry point for your plugin
92```
93
94Create a `app.config.js` (the entry point for a config plugin):
95
96```js
97module.exports = require('./plugin/build');
98```
99
100Create a `plugin/tsconfig.json` file. Notice that this uses `tsconfig.plugin` as the base config:
101
102```json
103{
104  "extends": "expo-module-scripts/tsconfig.plugin",
105  "compilerOptions": {
106    "outDir": "build",
107    "rootDir": "src"
108  },
109  "include": ["./src"],
110  "exclude": ["**/__mocks__/*", "**/__tests__/*"]
111}
112```
113
114In your `plugin/src/index.ts` file, write your TypeScript config plugin:
115
116```ts
117import { ConfigPlugin } from '@expo/config-plugins';
118
119const withNewName: ConfigPlugin<{ name?: string }> = (config, { name = 'my-app' } = {}) => {
120  config.name = name;
121  return config;
122};
123
124export default withNewName;
125```
126
127> �� Tip: Using named functions makes debugging easier with `EXPO_DEBUG=true`
128
129Optionally, you can add `plugin/jest.config.js` to override the default project Jest preset.
130
131```ts
132module.exports = require('expo-module-scripts/jest-preset-plugin');
133```
134
135Use the following scripts to interact with the plugin:
136
137- `yarn build plugin`: Build the plugin.
138- `yarn clean plugin`: Delete the `plugin/build` folder.
139- `yarn lint plugin`: Lint the `plugin/src` folder.
140- `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.
141- `yarn prepare`: Prepare the plugin and module for publishing.
142
143### �� Jest
144
145The Jest preset extends [`jest-expo`](https://github.com/expo/expo/tree/master/packages/jest-expo) or [`jest-expo-enzyme`](https://github.com/expo/expo/tree/master/packages/jest-expo-enzyme) and adds proper TypeScript support and type declarations to the presets.
146
147**For unit testing API-based modules:**
148
149```json
150{
151  "jest": {
152    "preset": "expo-module-scripts/universal"
153  }
154}
155```
156
157**For unit testing component-based modules:**
158
159```json
160{
161  "jest": {
162    "preset": "expo-module-scripts/enzyme"
163  }
164}
165```
166
167### �� LICENSE
168
169This makes it easier for other members of the community to work with your package. Expo usually has the **MIT** license.
170
171```json
172{
173  "license": "MIT"
174}
175```
176
177### Side Effects
178
179The [`@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`).
180
181[**Learn more about side effects**](https://webpack.js.org/guides/tree-shaking/)
182
183```json
184{
185  "sideEffects": false
186}
187```
188
189### Entry Point and Types
190
191We recommend you name the initial file after the module for easier searching. Be sure to define the `types` file as well.
192
193> �� Note that the `"typings"` field is synonymous with `"types"` field, Expo uses the TypeScript preferred `"types"` field.
194
195[**Learn more about "types" field**](https://webpack.js.org/guides/tree-shaking/)
196
197```json
198{
199  "main": "build/Camera.js",
200  "types": "build/Camera.d.ts"
201}
202```
203
204> �� 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).
205
206### �� npm Linking
207
208Make your package accessible to npm users by adding the following fields:
209
210Expo modules use the long form object when possible to better accommodate monorepos and hyperlinks:
211
212- [homepage docs](https://docs.npmjs.com/files/package.json#homepage)
213- [bugs docs](https://docs.npmjs.com/files/package.json#bugs)
214- [repository docs](https://docs.npmjs.com/files/package.json#repository)
215
216```json
217{
218  "homepage": "https://github.com/YOU/expo-YOUR_PACKAGE#readme",
219  "repository": {
220    "type": "git",
221    "url": "git+https://github.com/YOU/expo-YOUR_PACKAGE.git"
222  },
223  "bugs": {
224    "url": "https://github.com/YOU/expo-YOUR_PACKAGE/issues"
225  }
226}
227```
228
229## ⌘ Commands
230
231This 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:
232
233```sh
234$ cd expo-example-module
235$ yarn expo-module test
236
237# For commonly run commands, add "expo-module test" as an npm script named "test"
238$ yarn test
239```
240
241For scripts that need to run as part of the npm lifecycle, you'd invoke the commands from npm scripts in package.json:
242
243```json
244{
245  "scripts": {
246    "prepare": "expo-module prepare",
247    "prepublishOnly": "expo-module prepublishOnly"
248  }
249}
250```
251
252These are the commands:
253
254### configure
255
256This generates common configuration files like `tsconfig.json` for the package. These auto-generated files are meant to be read-only and committed to Git.
257
258### typecheck
259
260This type checks the source TypeScript with `tsc`. This command is separate from `build` and does not emit compiled JS.
261
262### build
263
264This 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.
265
266If 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.
267
268#### build plugin
269
270Running `build plugin` builds the plugin source code in `plugin/src`.
271
272### test
273
274We 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.
275
276If we were to use just Babel with the TypeScript plugin for the `build` command, Jest with `babel-jest` would be more closely aligned.
277
278### lint
279
280This runs ESLint over the source JS and TypeScript files.
281
282One 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):
283
284> If you are consuming the code here and you are not also a Facebook project, be prepared for a bad time.
285
286Replacements for common `fbjs` uses-cases are listed below:
287
288- `invariant`- replace with [`invariant`](https://www.npmjs.com/package/invariant)
289- `ExecutionEnvironment`- replace with [`Platform` from `@unimodules/core`](https://github.com/expo/expo/blob/master/packages/%40unimodules/react-native-adapter/src/Platform.ts)
290
291#### lint plugin
292
293Running `lint plugin` will lints the plugin source code in `plugin/src`.
294
295### clean
296
297This deletes the build directory.
298
299#### clean plugin
300
301Running `clean plugin` will delete the `plugin/build` directory.
302
303## Lifecycle Commands
304
305These are commands to run as part of [the npm scripts lifecycle](https://docs.npmjs.com/misc/scripts).
306
307### prepare (npm lifecycle)
308
309Runs `clean` and `build`.
310
311### prepublishOnly (npm lifecycle)
312
313Runs `npm-proofread`, which ensures a [dist-tag](https://docs.npmjs.com/cli/dist-tag) is specified when publishing a prerelease version.
314
315## Excluding Files from npm
316
317By 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.
318
319## Unified Dependencies
320
321This 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.
322