tracker1 1 day ago. link 1 point ▲ ▼(also posted on the medium article as a comment) First, I think that flow is pretty much a dead end. I know that it's backed and used by Facebook, so will probably be around for a while, but have the distinct impression that TypeScript has won out on this, and that the broader npm module systems have more thorough support for TS. TS has over 8m downloads a week, while Flow has around 16k. Second, on if it's worth it, depends on how many developers and of what skill level you are working with. Beyond this, what kind of structure you enforce not to mention other potential aids/rails like code coverage for testing, etc. TS does allow for a nicer refactoring workflow, you break things and fix the breaks when you refactor. JS requires a more judicious approach, which isn't bad if you start with a clean directory/module structure and keep your code testable. To that last part, code coverage and testing help ensure, but do not guarantee a cleaner approach. Personally, I find that I don't gain from having typed code in JS. That said, I can see the advantage on some projects/teams that are less experienced, or more likely to have different approaches on a project lifetime. It is not a replacement for clean or testable code. Aside, I'm also not a fan of the class approach in general and prefer more function based modules/libraries that act on general objects (can use interfaces in TS).