Use declaration merging.
If, say, you are using a third party JS script that attaches on to the
window global, you can extend
Likewise if you wish to "import" an image or other non TS/TSX file:
tsc cannot bundle these files for you, you will have to use Webpack or Parcel.
Related issue: https://github.com/Microsoft/TypeScript-React-Starter/issues/12 and StackOverflow