Setup

Docusaurus supports writing and using TypeScript theme components. To start using TypeScript, add @docusaurus/module-type-aliases and some @types dependencies to your project:
npm install --save-dev typescript @docusaurus/module-type-aliases @types/react @types/react-router-dom @types/react-helmet @tsconfig/docusaurus
Then add tsconfig.json to your project root with the following content:
{
  "extends": "@tsconfig/docusaurus/tsconfig.json",
  "include": ["src/"]
}
Docusaurus doesn't use this tsconfig.json to compile your project. It is added just for a nicer Editor experience, although you can choose to run tsc to type check your code for yourself or on CI.
Now you can start writing TypeScript theme components.

Swizzling TypeScript theme components

For themes that supports TypeScript theme components, you can add the --typescript flag to the end of swizzling command to get TypeScript source code. For example, the following command will generate index.tsx and styles.module.css into src/theme/Footer.
npm run swizzle @docusaurus/theme-classic Footer --typescript
At this moment, the only official Docusaurus theme that supports TypeScript theme components is @docusaurus/theme-classic. If you are a Docusaurus theme package author who wants to add TypeScript support, see the Lifecycle APIs docs.