Example project showing how to use babel with TS with pipelines. Here TypeScript is just used for typechecking. Since we need to run a babel pass before the code is ready for TypeScript, it won't work in the editor, just on the command line.

npm run build does a normal build (and no type-checking).

npm run check does a babel compile that just removes pipelines (and optional chaining and throw expressions).

npm run check-watch does the same using --watch for both babel and TypeScript.

npm run check-and-build-watch does both the TS typechecking and full builds using babel.

How it works

There are two different configurations for babel.

babel.config.for_typescript.js is just for removing things that TypeScript can't handle, like pipelines. That is then compiled to ts_check/src_from_babel. Then we run tsc --project ts_check/tsconfig.json, which has "noEmit": true, so nothing happens but typechecking.

babel.config.for_web.js does a normal build and no type-checking.

npm run check-and-build-watch will be running three processes in parallel:

• One babel process from src to ts_check/src_from_babel, translating only syntax TS can't handle.
• One TypeScript process looking at ts_check/src_from_babel and reporting type errors when the first process writes changes to it.
• One babel process from src to lib, doing a full translation.