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Facebook Launches Flow, Static Type Checker for JavaScript

code.prod.facebook.com

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Re: Facebook Launches Flow, Static Type Checker for JavaScript

#71

Post by jamesgpearce »

inglor wrote: post #57
kmavm wrote: post #52

Earlier quoted context omitted.

Thanks for the kind words. For context, I'm an HHVM alum who has been at Facebook for almost six years now (wow time flies). From my point of view, most of what has changed is resources and the immediacy of our survival-level concerns. Four years ago Google had declared nuclear war on us, we had far fewer users, we were not profitable, there were constant fires to put out with basic production operations stuff we've…

Thanks for answering, it's always good to get answers straight from the source. It would be awesome if you blogged about this. It would be interesting to read _how_ you got better at being good stewards of your open source projects and what made you open source these. I think it's a challenge a lot of people face.

This presentation at OSCON 2014 runs through some of the things we've tightened up: https://www.youtube.com/watch?v=fzL6Zoy_ndk

Re: Facebook Launches Flow, Static Type Checker for JavaScript

#72

Post by jallmann »

drderidder wrote: post #11

Static analysis is definitely preferable to cross-compilation and this looks like a great tool. That said, the idea that static type checking makes developers more productive and prevents tons of errors is overstated imho. Type inference is supposed to make coding simpler and more productive (particularly in functional languages) - even C++11 has added it. I'm sure static type checking can benefit some organizations,…

> the idea that static type checking makes developers more productive and prevents tons of errors is overstated

Then perhaps you are understating the importance of software correctness. While type systems can be an almost religious topic, the benefits of type checking are real -- a whole class of bugs to disregard, less testing code, and a more maintainable codebase for other developers. Moreover, for languages with ADTs and exhaustive type-checking, you are forced to reason about boundary and error conditions. All of which leads to higher quality software, at the minimal cost of up-front work when designing your types and fixing what the compiler/checker says.

> type related errors are usually easy to find and fix and have rarely if ever been the root cause of our most difficult problems.

Type related errors may be easy to diagnose and fix -- although by definition, in the absence of type-checking, type errors are only so after the fact, eg after causing a crash. Hence the utility of type checkers, especially if it means fewer avoidable errors appearing in production.

> Dynamic type checking and implicit conversion is one of the more powerful features of JavaScript and certainly no less prone to error or counter-productive than type-casting, making variadic functions or class templates are in other languages.

Type checking doesn't diminish the usefulness/convenience of dynamic languages, but IMO lends more weight to the benefits of strongly static languages -- benefits which are negated by the abuse of "features" such as typecasting or variadic functions.

Re: Facebook Launches Flow, Static Type Checker for JavaScript

#73

Post by Joeri »

drderidder wrote: post #11

Static analysis is definitely preferable to cross-compilation and this looks like a great tool. That said, the idea that static type checking makes developers more productive and prevents tons of errors is overstated imho. Type inference is supposed to make coding simpler and more productive (particularly in functional languages) - even C++11 has added it. I'm sure static type checking can benefit some organizations,…

Static analysis is somewhat like having very minimalistic type-only unit tests. If you already have comprehensive unit tests, you don't benefit much, but if you don't you really notice the quality difference in the code that ships when you run static analysis prior to shipping.

Re: Facebook Launches Flow, Static Type Checker for JavaScript

#75

Post by slashnull »

drderidder wrote: post #11

Static analysis is definitely preferable to cross-compilation and this looks like a great tool. That said, the idea that static type checking makes developers more productive and prevents tons of errors is overstated imho. Type inference is supposed to make coding simpler and more productive (particularly in functional languages) - even C++11 has added it. I'm sure static type checking can benefit some organizations,…

I like to think that static typing haven't delivered its promises because the current statically typed languages and toolage is inappropriate and immature, but I realize that this might be a symptom of the Smug LISP Weenie syndrome that affects me.

Re: Facebook Launches Flow, Static Type Checker for JavaScript

#76

Post by ep103 »

slashnull wrote: post #70
ep103 wrote: post #68

This looks like such a better step in the right direction than than the types of tools MS and Google have been putting out. Dynamically discerning the underlying code, and allowing optional type annotation works _with_ javascript, as opposed to attempting to turn js into a completely different (and weakened) language. That said, I am curious what solutions this solves that isn't already solved by enforcing good code…

So what's wrong with having a tool to automate those practices ; )

This is a bit off topic, but I digress....

I specifically didn't send this tool to the team I work on, because my team lead is a sql / java / c# guy who loves static languages, and only touches the front end with a stick if he has to, and then only some basic jQuery or angular.

I've sold him on jasmine and requiring front end test coverage, recently. But right before I hit the send button I realized that if I sent him this tool, I'd never be allowed to use dynamic typing or non annotated functions/arguments in js ever again.

Hence my question : /

Re: Facebook Launches Flow, Static Type Checker for JavaScript

#77

Post by dested »

ep103 wrote: post #68

This looks like such a better step in the right direction than than the types of tools MS and Google have been putting out. Dynamically discerning the underlying code, and allowing optional type annotation works _with_ javascript, as opposed to attempting to turn js into a completely different (and weakened) language. That said, I am curious what solutions this solves that isn't already solved by enforcing good code…

How does optional typing weaken javascript?

Re: Facebook Launches Flow, Static Type Checker for JavaScript

#78

Post by inglor »

ep103 wrote: post #68

This looks like such a better step in the right direction than than the types of tools MS and Google have been putting out. Dynamically discerning the underlying code, and allowing optional type annotation works _with_ javascript, as opposed to attempting to turn js into a completely different (and weakened) language. That said, I am curious what solutions this solves that isn't already solved by enforcing good code…

Well, here are some things that it does that other tools don't:

- It type checks JSX - It supports some ES6 features others don't (like destructuring) as the build step - It has union types (TS will get those soon, already in master) - It does a lot more inference and a lot more assumptions. It assumes you won't multiply a string by a number for example (although technically '10' * 5 is legal in JS). So it's opinionated in that it enforces checks that rule out code that is legal but not likely intended in JS (an opinin I agree with).

Yes - it is possible to write tests and get good coverage and not use those tools - however static analysis can be very valuable in finding errors early. While I'm not sure I'd bother with explicit typing in this in smaller projects from the examples and unit tests it looks like it could find errors people would not easily notice otherwise. (Think JSHint, on steroids).

That said, only time will tell how good the implementation will really get in understanding your code.

Re: Facebook Launches Flow, Static Type Checker for JavaScript

#79

Post by slashnull »

dested wrote: post #77
ep103 wrote: post #68

This looks like such a better step in the right direction than than the types of tools MS and Google have been putting out. Dynamically discerning the underlying code, and allowing optional type annotation works _with_ javascript, as opposed to attempting to turn js into a completely different (and weakened) language. That said, I am curious what solutions this solves that isn't already solved by enforcing good code…

How does optional typing weaken javascript?

I suppose he was talking about TypeScript and CoffeeScript.
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