react-native-typescript-transformer

Seamlessly use TypeScript with react-native >= 0.45

Stop! You probably don't need this package.

If you are starting a new React Native project, you can initialize the project with this command:

react-native init MyAwesomeProject --template typescript

This will set up the project to transpile your TypeScript files using Babel.

Otherwise, if you're using React Native 0.57+ and you are converting an existing RN app to TS, then you can follow the configuration in this gist: https://gist.github.com/DimitryDushkin/bcf5a7f5df71113c67dbe2e890008308

Babel Caveats

Babel will not type-check your files. You'll still want to use the TypeScript compiler as a kind of linter (with the noEmit compiler option set to true).

Also there are four rarely-used langauge features that can't be compiled with Babel.

From this blog post:

• namespaces
• bracket style type-assertion/cast syntax regardless of when JSX is enabled (i.e. writing <Foo>x won’t work even in .ts files if JSX support is turned on, but you can instead write x as Foo).
• enums that span multiple declarations (i.e. enum merging)
• legacy-style import/export syntax (i.e. import foo = require(...) and export = foo)

Don't expect this list to grow.

I'm on RN < 0.57 or I definitely want to compile my TypeScript files using TypeScript and not Babel

Step 1: Install

yarn add --dev react-native-typescript-transformer typescript

Step 2: Configure TypeScript

Make sure your tsconfig.json has these compiler options:

{
  "compilerOptions": {
    "target": "es2015",
    "jsx": "react",
    "noEmit": true,
    "moduleResolution": "node",
  },
  "exclude": [
    "node_modules",
  ],
}

See tsconfig.json Notes for more advanced configuration details.

Step 3: Configure the react native packager

RN >= 0.59

In your projects root, extend metro.config.js so it contains the transformer.babelTransformerPath property:

module.exports = {
  transformer: {
    babelTransformerPath: require.resolve('react-native-typescript-transformer')
  }
};

RN >= 0.57, < 0.59

Add this to your rn-cli.config.js (make one if you don't have one already):

module.exports = {
  transformer: {
    babelTransformerPath: require.resolve('react-native-typescript-transformer')
  }
}

RN < 0.57

Add this to your rn-cli.config.js (make one if you don't have one already):

module.exports = {
  getTransformModulePath() {
    return require.resolve('react-native-typescript-transformer');
  },
  getSourceExts() {
    return ['ts', 'tsx'];
  }
}

If you need to run the packager directly from the command line, run the following

react-native start --config /absolute/path/to/rn-cli.config.js

Step 4: Write TypeScript code!

Note that the platform-specific index files (index.ios.js, index.android.js, etc) still need to be .js files, but everything else can be TypeScript.

You probably want typings for react and react-native

yarn add --dev @types/react @types/react-native

Note that if you run yarn tsc it will act as a type checker rather than a compiler. Run it with --watch to catch dev-time errors in all files, not just the one you're editing.

Use tslib (Optional)

yarn add tslib

in tsconfig.json

 {
   "compilerOptions": {
+    "importHelpers": true,
   }
 }

Doing this should reduce your bundle size. See this blog post for more details.

Use absolute paths (Optional)

Absolute paths needs to have support from both the TypeScript compiler and the react-native packager.

This section will show you how to work with project structures like this:

<rootDir>
├── src
│   ├── package.json
│   ├── App.tsx
│   ├── components
│   │   ├── Banana.tsx
│   ├── index.tsx
├── index.ios.js
├── package.json
├── tsconfig.json

Where you want to be able to import Banana from 'src/components/Banana' from any .ts(x) file, regardless of its place in the directory tree.

TypeScript

In tsconfig.json:

 {
   "compilerOptions": {
+    "baseUrl": "."
   }
 }

react-native

For react-native you need to add one or more package.json files. These only need to contain the "name" field, and should be placed into any folders in the root of your project that you want to reference with an absolute path. The "name" field's value should be the name of the folder. So for me, I just added one file at src/package.json with the contents {"name": "src"}.

Jest (Optional)

If you use Jest as a test runner, add the following in your root package.json:

 {
   "jest" {
+     "modulePaths": ["<rootDir>"]
   }
 }

tsconfig.json Notes

• If you enable synthetic default imports with the "allowSyntheticDefaultImports" flag, be sure to set "module" to something like "es2015" to allow the es6 import/export syntax to pass through the TypeScript compiler untouched. Then Babel can compile those statements while emitting the necessary extra code to make synthetic default imports work properly.

  This is neccessary until TypeScript implements suport for synthetic default imports in emitted code as well as in the type checker. See Microsoft/TypeScript#9562.

• "target" can be anything supported by your project's Babel configuration.

• "jsx" can also be "react-native" or "preserve", which are functionally identical in the context of a react-native-typescript-transformer project. In this case, the JSX syntax is compiled by Babel instead of TypeScript

• The source map options are not useful

• You probably want to specify some base typings with the "lib" option. I've had success with the following:

   {
     "compilerOptions": {
  +    "lib": [ "es2017" ],
     }
   }

  Including the "dom" lib is not recommended. The React Native JavaScript runtime does not include any DOM-related APIs. See JavaScript Environment for more details on what web APIs React Native supports.

Jest notes

Follow the react-native setup guide for ts-jest.

Alternatively, if you want to use exactly the same transformation code for both Jest and react-native check out this comment.

Note that there have been no reports of problems arising from differences between code compiled by the ts-jest transformer and code compiled by react-native-typescript-transformer. Additionally, ts-jest takes care of a lot of edge cases and is more configurable.

Avoid cyclical dependencies

If you're transitioning an app from tsc to react-native-typescript-transformer, you might see runtime errors which involve imported modules being undefined. You almost certainly have cyclical inter-module dependencies which manifest during your app's initialization. e.g. if ModuleA is undefined in ModuleB it means that ModuleA (in)directly imports ModuleB.

tsc seems to be able to mitigate some instances of these cyclical dependencies when used as a whole-app compiler. Unfortunately the module-at-a-time compilation approach that react-native's bundler supports does not permit the same optimizations.

Be especially careful of "umbrella export" files which can easily introduce these cycles.

License

MIT