Migrate a JavaScript Nodejs project to TypeScript

1. if using create-react-app, eject it so you can edit the tsconfig.json freely. It also allows index.ts to behave correctly when you use “export * from ‘./component”.
2. rename .js files to .ts files
3. refactor import and export. Prefer named exports, avoid using default export.
4. (for nodejs) if you put db object on the Request, use declaration merging to add db to the Request. Good article here: https://dev.to/kwabenberko/extend-express-s-request-object-with-typescript-declaration-merging-1nn5
5. if you use a npm module that don’t have a type defined, you can use following method to make the type error goes away:

for frontend tsconfig.json:
{
  "compilerOptions": {
    "paths": {
      "*": [
          "node_modules/*",
          "src/typings/*"
      ]
    }
  }
}
for nodejs tsconfig.json:
{
  "compilerOptions": {
      "typeRoots": [
          "src/types",
          "./node_modules/@types"
      ],
      "baseUrl": "./src",
  }
}

then do something like this: