[robinricard]

Both systems are really great, however, when adding typechecking into an existing codebase, flow does offer more flexibility thanks to weak checking and annotation comments. You can really progressively add typechecking by just dropping the tool in the codebase. Also, if you subscribe to Facebook's tooling (Nuclide especially), you will end up with great tools (jump to def, integrated checking, ...). However if you just start the project and you use VSCode, TS seems to be a strongest choice. Depends on what you do, but both tools are great, whatever you choose, typechecking is worth in javascript if you need more reliability and maintainability.

[hoodunit]

I actually found the opposite was true in our project - TypeScript was easier to add into the code than Flow. The biggest reason for this was that Flow demands null/undefined checking and null was used extensively throughout this code base. With TypeScript, on the other hand, the changes to make it work initially amounted to sprinkling a few "any" notations and making some explicit object interfaces at various points.

[shados]

Flow supports nullable types just fine, and flow in weak mode doesn't mandate any annotation whatsoever.