[wozer]

Agree.

Typescript doesn't have real algebraic data types becauses at the end of the day, Typescript is just a statically-typed version of Javascript. And Javascript doesn't have adts.

For me, the biggest advantage of static typing is that code is much more self-documenting. Also, refactoring becomes much easier.

[Too]

Refactoring type safe code vs non type safe code is like night and day. We had a code base in js where even minor refactoring meant frenetic greping and manually replacing things a whole day, fixing problems for a week and occasionally getting a remaining bug on the production site a month after that. We rewrote the whole thing to typescript and after that you could do major refactoring in just minutes and be quite sure that nothing else would break. Also during the rewrite, the compiler always pointed out at least one potential bug in each file, this was quite funny to see because we already considered our old js-code to have quite high quality.

The whole code browsing experience is just different, you can actually read partial sections of the code base and understand them, use code completion, "go to definition" and "find all usages" and it works reliably. Not using types is in my book professional misconduct.

His comparison with C#/Java is also very weird and shows he hasn't given it a proper try. The ducktyping nature of interfaces makes the code much less rigid than in java but still maintains most of the safety you need.

[shados]

Generally when TypeScript is compared to C#/Java, it is about the syntax look, or when contrasting it to other type system such as, let say, Scala. And then it's very much on the C#/Java side of the fence.

TypeScript definitely got the structural checking of interfaces right, but I beleive (correct me if I'm wrong, I'm referring to https://github.com/Microsoft/TypeScript/issues/202) that classes are also structurally checked. Flow does nominal checking for those, with very good reasons.

While it's a shame the details are light because you kind of need the presenter to go with the slides, the following explains a few of the reasons between TypeScript vs Flow:

http://www.scs.stanford.edu/16wi-cs240h/slides/fb-slides.htm...

(not the whole deck, just a few slides after 45)

[spicyj]

For comparison, Flow supports tagged unions like this:

http://flowtype.org/blog/2015/07/03/Disjoint-Unions.html

[Arnavion]

TS has string types starting from 1.8, although they can't be used for narrowing down the type yet in the way that Flow can.

http://bit.ly/1LhA5id