I've been working with TS for the past couple of years but now I'm working on a Flow project.
Flow doesn't even compare. It falls short on many things TS would immediately flag, and just feels less thought-out (subjective I know). Tooling support is terrible and while not the language's fault, it means it just doesn't help you as much as it could. Using Flow basically becomes an afterthought, a part of your build step, while with TS it's much easier to have that integrated into your development flow (via your editor of choice).
And honestly, some of the decisions around the language just feel strange. Not knowing what kind of bool to use [0] is pretty emblematic of where it is going as a language.
To me Flow is just half-helping in a way that TS is fully devoted to.
[0] http://stackoverflow.com/questions/40618817/flow-bool-boolea...
I'm kind of curious what you've run into personally. Having a dependency without any type-defs get silently treated as `any` is my own beef, but I haven't hit much else yet.
(Some type-defs' use for `any` also gets my goat, such as Promise's catch argument and some of the lodash functions, but I'm considering that a separate thing.)
> And honestly, some of the decisions around the language just feel strange. Not knowing what kind of bool to use [0] is pretty emblematic of where it is going as a language.
This is more an existing JS weirdness (`true`/`false` vs `Boolean()`); Flow doesn't mess with runtime semantics, only adding a layer that you check with then strip out.
And TypeScript has the same thing:
var a: boolean = new Boolean(1);
// Produces:
// NewTypering.ts(29,5): error TS2322: Type 'Boolean' is not assignable to type 'boolean'. Type 'Boolean' is not assignable to type 'boolean'.
'boolean' is a primitive, but 'Boolean' is a wrapper object. Prefer using 'boolean' when possible.You can add the compiler flag --noImplicitAny to get errors if you prefer.
".... at least if they use flow, they are bagging up their shite which is better than a open field of the stuff".
TypeScript absolutely has the better tooling. It's not even -close-. It's a little tricky though because a lot of FE devs these days use VIM or Sublime with a few plugins and a linter running in a terminal is as far as it goes, so explaining the importance of proper refactoring tool and semantic search is tough (no, using grep/ag/ack is not enough in a large code base, no matter how good you are with them).
On the other hand, the Flow checker is a lot more interesting, with more advanced call site analysis, and the type inference follows types a lot further (where you can type an entire file without any annotations, though Flow does require them on exports if you want imports in other files to be typed). That means functions with no annotations are much more frequently type checked and it's more useful during prototyping.
Flow is also a bit more careful about putting on the C#/Java lipstick (neither Flow nor TypeScript are actually java/C#-like, being much more functional and using structural typing as first class citizens, but TypeScript definitely LOOK the part to the untrained eyes, which makes developers used with those languages try to use the same patterns and heavily abuse classes instead of union types, etc. In Flow it's less of an issue).
Flow definitely causes a lot more surprises: call site analysis means error messages can be more confusing, and certain cases like inaccessible code path can cause some surprising scenarios.
flow-typed has many less type definitions, but they're generally higher quality. TypeScript's type definitions I found are very, very poor, as a relic of the days where versioning was an issue and many have not been fixed. You also have issues with useStrictNull not having been there all along causing problems. TypeScript however benefits heavily from having more libraries being native TypeScript, which is better than having good type definitions.
Finally, while TypeScript's tooling is vastly superior, Flow has the benefit of being parsable by Babel via Babylon, making large parts of the ecosystem a lot more Flow friendly. This came up recently with the amazing Prettier project being a non-starter for TypeScript users.
I've been hopping between vanilla JS, Flow and TypeScript continually...and no matter which one I use, I wish I was using another.
I've always found it funny that DefinitelyTyped's tag line is "The repository for high quality TypeScript type definitions", but it's an absolutely disastrous system. If it's not a well-used library, definitions there will be woefully out of date. Versioning is a huge issue with it, so it's hard to figure out what definitions actually match the version library you're using. I can only admit that it's an effort that's better than nothing.
The few projects I added types to, the original project owners gladly accepted them into their main repos, which is great since types will "just work" without fuddling with @types packages.
When you start talking about getting into code bases that you didn't personally write. The time savings and productivity benefits that TypeScript brings are immense.
A lot of typings are now directly inside the NPM packages of the libraries themselves and install "automatically" for you; many other typings can be searched on NPM (primarily the @types/ scope).
It still feels like very much in beta. Things break often along the edges, there are things like interfaces that work only sometimes, the modules are always working strangely
Also, and that might be a personal thing, but for me, TypeScript itself has a more readable source code, since it's in TypeScript. Flow is in OCaml, which I cannot read.
On the other hand, I like how Flow is very "thin", and how I am just using ES6 with types "hints" on top; that's why I prefer Flow.
1. it often fails to find the type for an imported piece of code 2. more often than not refers to the type definition being a problem rather than whoever's calling a function with an incorrect type 3. it seems to have an issue with cache busting(?) (I `killall flow` multiple times per day to make sure it's not complaining about old code)
All in all I feel very sad for choosing Flow over TypeScript two weeks ago. We felt TS would be more invasive to our Webpack pipeline but I think I might just take a weekend to migrate over to TS...
TS seems to have a lot more type definitions available as well, a more active community perhaps?
Looking at the issue list of Flow I'm starting to suspect they're not very active in maintenance / issue handling. TS seems much more active.
It does a decent enough job at return types, but not a whole lot beyond that.
function double(x) {
return x * 2;
}
const result = double("foo");
If you target ES6 your code may look identical. Even much of the ES5 down leveling produced code that looks like a person wrote it.
I converted a 10k line coffeescript project(with async/await !) to JS and then TypeScript. The similarities are so far apart they might as well be in different dimensions. But, if you don't want to take a rando posters word for it, it's pretty easy to make a little sample project and see if the output is to your liking.
I think you're vastly misinterpreting what TS is.
It's not anything like CoffeeScript. It's JS plus types and a few other features like Interfaces or advanced ECMAScript features when targetting older versions of the standard.
If you strip away types by exporting to your ECMAScript target of choice, you'll get real JavaScript with the same style as it was written in TypeScript.
It's exactly the same thing you'd get with Flow in that sense. The only additional code you'd get would be for polyfills, but a) those are minimal and b) those will only appear if you export to an older ECMAScript version than the one you wrote it in.
There is no vendor lock.
That's about it though.
The same can be done to it that would be done to Flow: you can just either strip types manually, or just do a single export to your ECMAScripttarget of choice. It'll be native JavaScript. Even the little shims/polyfills it does (to support older ECMAScript versions if you wish to export to it) are optional and can be disabled.
It's open source.
> you can just strip all type annotations with Babel and move on.
Are you implying that this isn't possible with TypeScript?
https://github.com/Microsoft/TypeScript/wiki/JSDoc-support-i...
Honestly this is the main thing keeping me from using TypeScript. I've spent hours, maybe days trying to deal with the mess of Babel/webpack/TS combined with ES6 modules (necessary for tree shaking).
Another problem I ran into was using various packages that weren't typed, but I suppose I can solve that by 'allowing' implicitAny.
I'd really love some advice on this because I want to use TypeScript. It's just been a major headache so far because things are complicated enough with all the other moving parts (Babel presets, import vs require, better but still not well documented Webpack 2, etc.).
You can keep noImplicitAny and any-type just specific packages that can't/won't be typed. The declaration is now as simple as:
declare module 'path/to/module-name'
Where the plugins shine is when compiling those (part of the standard) features to something interesting for production. Better inlining, adding debugging and instrumentation, compiling away certain things, optimizing your views for performance, etc.
All things that don't change the language whatsoever, but can improve your debugging or production experience.
That can be done in TS world (and is quite common) by targeting ES6 and piping the result in Babel though. It's just annoying.
You do have things like Prettier not being compatible with TS because different parsers, though.
It's our intention as a tool to align with TC39 and transition users to using native JS when it's supported
- When typescript came out, I was an early adopter, and a lot of it's touted benefits were the class-like syntax and constructors to make it more palatable to enterprise shops (not for me, but it was easier to sell to higher ups), this is mostly a moot point now.
- flow can be attached to any codebase as the codebase stands easily. It is, I have found, difficult to bring TS into an existing project.
- flow fits nicely into existing popular js tooling, mainly babel and react.
- no risk of vendor lock in. Maybe TS compiles to pure 100% syntactically correct javascript today, maybe it doesn't in the future. It isn't javascript, so I won't know.
> - You are writing javascript, not typescript.
Flow's and TypeScript's distance to JS world are the same, and are very similar in most cases. If you want to add type to one, it's the same as in the other. The only difference here is the file extension, since TS tends to like .ts/.tsx.
> - When typescript came out, I was an early adopter, and a lot of it's touted benefits were the class-like syntax and constructors to make it more palatable to enterprise shops (not for me, but it was easier to sell to higher ups), this is mostly a moot point now.
True, although IMO the greatest feature of TS is making your code stronger, not compiling things that are already part of some ECMAScript version.
>- flow can be attached to any codebase as the codebase stands easily. It is, I have found, difficult to bring TS into an existing project.
True, with TS it's more of a lateral move rather than drops here and there.
>- flow fits nicely into existing popular js tooling, mainly babel and react.
TS works just as well; better, IMO, because dev tools (editors, linters) have better TS support in my experience. Writing React in JS to me makes me feel like I'm using Notepad since there's so much TS helps me with that is lost when using a purely dynamic language.
>- no risk of vendor lock in. Maybe TS compiles to pure 100% syntactically correct javascript today, maybe it doesn't in the future. It isn't javascript, so I won't know.
It does compile to pure JS so ejecting TS is easy; it's trying to follow future standards and proposed changes, not create something different; the project is open source. There is no vendor lock in.
And it's worth noting that TypeScript having its own parser vs the rest of the world using Babel is a pain in the rear. See the time it took for ESLint (having to us TSLint in the meantime), now Prettier, having to use TypeScript with an ES6 target and piping the output in Babel to get proper plugin support, the difference between webpack's resolution mechanism and the one used by TypeScript in tools (an issue Flow also shares), and so on.
Some features like enums (omg, TS enums die die die) namespaces, decorators, and the old module system are also pretty awkward when blending with modern javascript. Makes you want to add lint rules to prevent them from being used.
// @param somestring [String] yadda yadda
// @return [Boolean]
function somefunction(somestring) {
// @type [Boolean]
var ret;
...
return ret;
}
function somefunction(somestring/*: string*/)/*: boolean */ {
var ret/*: boolean */;
...
return ret;
}
It can also build really nice HTML documentation to.
[1]: https://flowtype.org/blog/2015/02/20/Flow-Comments.html
[2]: https://github.com/Khan/aphrodite/blob/master/src/generate.j...