React + TS: How to introduce TypeScript to old React project

README.md

Steps

• add tsconfig.json and remove jsconfig.json
• change index.js to index.tsx
• install dependencies: yarn add typescript @types/node @types/react @types/react-dom @types/jest --dev
• make test component like Test.tsx and check if typescript works there

Troubleshooting

Problem with relative paths

If your project uses relative-to-root instead of relative-to-current-file paths like below:

import routes from 'domain/routes';

You should add this to the tsconfig.json: "baseUrl": "./src", Then in all the descendant directories you can use paths like tools/something instead of ../../../tools/something

tsconfig.json

{
  "compilerOptions": {
    "module": "esnext",
    "target": "es5",
    "allowJs": true,
    "checkJs": false,
    "jsx": "react-jsx",
    "outDir": "./build",
    "rootDir": "./src",
    "baseUrl": "./src",
    "removeComments": true,
    "noEmit": true,
    "pretty": true,
    "skipLibCheck": true,
    "strict": true,
    "moduleResolution": "node",
    "esModuleInterop": true,
    "lib": [
      "dom",
      "dom.iterable",
      "esnext"
    ],
    "allowSyntheticDefaultImports": true,
    "forceConsistentCasingInFileNames": true,
    "noFallthroughCasesInSwitch": true,
    "resolveJsonModule": true,
    "isolatedModules": true
  },
  "include": [
    "./src/**/*"
  ],
  "exclude": [
    "node_modules"
  ]
}