Setting up Babel and TypeScript

README.md

Install Babel 7 and TypeScript

yarn add --dev \
  @babel/core \
  @babel/cli \
  @babel/preset-env \
  @babel/preset-typescript \
  typescript

Babel config

Configure babel.config.js to add preset-typescript in there.

module.exports = {
  presets: ['@babel/preset-typescript', '@babel/preset-env']
}

TypeScript config

Create tsconfig.json.

{
  "compilerOptions": {
    // Target latest version of ECMAScript.
    "target": "esnext",
    // Search under node_modules for non-relative imports.
    "moduleResolution": "node",
    // Process & infer types from .js files.
    "allowJs": true,
    // Don't emit; allow Babel to transform files.
    "noEmit": true,
    // Enable strictest settings like strictNullChecks & noImplicitAny.
    "strict": true,
    // Import non-ES modules as default imports.
    "esModuleInterop": true,
    "jsx": "react"
  },
  "include": [
    "src" // <-- change this to where your source files are
  ]
}

Add tsc script

Add the tsc script to your package.json. Configure your CI to run yarn run tsc for checks.

"scripts": {
  "watch": "babel --watch src ---out-dir lib --extensions '.ts,.tsx'",
  "build": "babel src --out-dir lib --extensions '.ts,.tsx'",
  "tsc": "tsc"
}

Just run tsc

This will run type checks.

yarn run tsc

Also see

• https://blogs.msdn.microsoft.com/typescript/2018/08/27/typescript-and-babel-7/

For anyone else who still has some js and jsx files in their project along with ts and tsx files you can use the following in your package.json:

"scripts": {
  "watch": "babel --watch src ---out-dir lib --extensions '.js,.ts,.tsx,.jsx'",
  "build": "babel src --out-dir lib --extensions '.js,.ts,.tsx,.jsx'",
  "tsc": "tsc"
}

There is an extra - in --out-dir. Don't forget to remove it as well.