Expo

Documentation

Using TypeScript

TypeScript - "JavaScript that scales." TypeScript is a superset of JavaScript which gives you static types and powerful tooling in Visual Studio Code.
We are currently in the process of updating our entire SDK to use TypeScript and we will provide first class support in the very near future. For the moment, support is provided through the Expo user community maintained Expo SDK type definitions, which you can contribute to here if you encounter any deficiencies. Now let's walk through how to set up TypeScript on a blank Expo app initialized through expo-cli. If you'd rather just jump right ahead to the finished result, you can clone this repository.

We need to install three packages: the typescript compiler, the expo type definition and the react-native type definition.
npm install --save-dev typescript@^3.3.0 @types/expo@^32.0.0 @types/react-native@^0.57.0

Create a file in the root of your project called tsconfig.json and put this in it:
{
  "compilerOptions": {
    "allowSyntheticDefaultImports": true,
    "jsx": "react-native",
    "lib": ["dom", "esnext"],
    "moduleResolution": "node",
    "noEmit": true,
    "skipLibCheck": true
  }
}
For information on these properties, see the tsconfig.json documentation.

Let's rename App.js to App.tsx. We use the .tsx extension because the file includes React components (using JSX). If the file did not include any React components, we should use the .ts file extension.

Now everything is ready and you can run expo start and open the app. If you open the project in Visual Studio Code and start working on it, you will see that suddenly the editor is much more helpful than before - autocompletion and suggestions, useful warnings when you making a typo, annoying warnings when you think you're doing something correctly but actually you're not, etc. Enjoy, and read the TypeScript Handbook to continue your journey to learning TypeScript.