[domlebo70]

> This has the incredible effect of making it a type error if you try to execute an action that doesn't exist.

I don't want to start a "JavaScript is bad" flamewar, but it's sad that there is an entire class of problems that we as software developers are solving, where simple type checking seems amazing

[nathan_f77]

Sure, but with ES2016 and Flow, JavaScript becomes a completely different language. And with V8, it's very fast. I actually really enjoy writing JavaScript now, and I recently realized that I like it more than Ruby.

[STRML]

Yes - and no. Flow can express some really complex types that were previously only possible in much more esoteric (or modern) languages. Types as many people know them from Java, C#, etc., are more mature (aka fewer bugs), but far less powerful.

For example:

The utility types in https://flow.org/en/docs/types/utilities/ can be used to great effect to express things like "A type of the keys of T, but values passed through this function" or "A type that is the difference of these two maps".

In practice, this helps me write things like React Components that take some of their props from the root store via context, and the rest of their props directly, and for Flow to actually know which is which just by reading the code (no explicit typedefs!), override root store props as needed (so long as I don't change their types), and throw a type error if I miss or misdefine one. Awesome.