Microsoft/TypeScript

TypeScript is a superset of JavaScript that compiles to clean JavaScript output.

Thanzex

@Thanzex

What are the best practices to export constants from a package?

Anthony Lukach

@alukach

Does TS not allow typing a function without directly calling it?

e.g.

[{x: 1}].map(Object.entries<number>) // 'number' only refers to a type, but is being used as a value here.

Bruce Pascoe

@fatcerberus

Yeah, you can’t instantiate the generic without calling the function, we were discussing that here recently

Keith Layne

@keithlayne

if you could....

Bruce Pascoe

@fatcerberus

It actually seems like it’s interpreting the angle brackets as comparison operators there, which is odd

Anthony Lukach

@alukach

Is it clear what I'm trying to do? This would be helpful for composing "point free" functions (I'm using ramda). WIthout adding a type to Object.entries, TS thinkings the 1 index of the tuple is any rather than number... Is there a way to achieve my goal?

Keith Layne

@keithlayne

yeah, we all understand what you want

Anthony Lukach

@alukach

@fatcerberus On TS playground, for whatever reason it's actually changing Object.entriesto Object.entries(): http://www.typescriptlang.org/play/#code/NobwHgXABAjAvgXQHQFsCGAHAFAeQEYBWApgMYAuSRAdmQE4CWRAzgDxUCuKeRtAfAJRQA9EKgByDlx5ioAeyoAbAJ5RaRAGY8mUMrKhodSjEQA0UPOzJR627vSoBzKOyZEAJvu0GAbmgXsiKAALHiIkIA

Keith Layne

@keithlayne

write a lambda where you specify the type

Anthony Lukach

@alukach

well that's not much fun, but if that's the way it has to be...

Keith Layne

@keithlayne

for your own functions you can sort of work around by writing a generic interface with a call signature.

Bruce Pascoe

@fatcerberus

The compiler sees a syntax error in reality but it always tries to recover and emit valid code so that makes sense

Keith Layne

@keithlayne

whoosh

Bruce Pascoe

@fatcerberus

Huh?

Anthony Lukach

@alukach

@fatcerberus :thumbsup: Oops, I spaced the error about Property 'entries' does not exist on type 'ObjectConstructor'.

Thanzex

@Thanzex

I'm trying to create a package to export some constants and interfaces that we need for a project. The interfaces work just fine, but trying to import and use one of the exported constants gives an error in compilation with webpack.
WARNING in ./src/app/app.component.ts 6:17-20 "export 'CONSTANT' was not found in 'package'
My package is made of:
constants.ts

export const TEST="test";

index.js

import { TEST } from './constants'

module.exports = { TEST }

index.d.ts

export { TEST} from './constants'

After searching for a while i found webpack/webpack#7378 that seems to dive into the problem but i haven't found a soultion yet.
Any ideas?

Keith Layne

@keithlayne

you need to export { TEST } from './constants'

Thanzex

@Thanzex

yup sorry, i re-wrote everything for the message, there are no typos

Keith Layne

@keithlayne

and in the types. Not sure what your mixed case meant. Okay.

Do you have a constants.d.ts?

and are you exporting the constant in JS somewhere?

Thanzex

@Thanzex

in the message i forgot to add the module exports in the js file

@keithlayne what do you mean?

i do not have a constants.d.ts

Keith Layne

@keithlayne

well you're referencing it.

Thanzex

@Thanzex

i do have many more files that contain only interfaces without the *.d.ts file and they work fine with this setup

Keith Layne

@keithlayne

are you writing in mixed js/ts?

Thanzex

@Thanzex

nope, only ts, but the package started as a normal js one

Keith Layne

@keithlayne

if you have tsc emit your declarations you shouldn't have a problem I think.

Unless it's something weird that I don't understand, which is totally possible.

what I was getting at is that tsc will generate a .d.ts per .ts file, and they'll reference each other just like the JS files.

I'm still not clear if you're writing those declarations by hand or not.

Thanzex

@Thanzex

in the issue that i referenced i foud out about isolatedModules. Apparently if you declare a constant in a file and export it, export it fro another file again like export { foo } from './bar' it's like the declaration doesn't exist

it was all done by hand

Keith Layne

@keithlayne

yeah you shouldn't do that, especially when tsc can do it for you. Why isolatedModules? Using babel or something?

sorry, got a meeting for now

Thanzex

@Thanzex

yup, using webpack

sorry, forgot to add

Keith Layne

@keithlayne

yeah I never really use any bundlers on npms. I can imagine some use cases, but I generally let the consumer decide if/how to bundle.

Bruce Pascoe

@fatcerberus

You can't do export from with isolatedModules afaik

With that setting on the compiler is basically looking at each file individually so it's not able to thread the types through

Since you're using webpack I recommend disabling isolatedModules and using ts-loader

Then webpack will compile the TS directly as part of the build

No need for a pre-transpile step

Andrew Hodges

@betawaffle

Is there a reason something like this isn't in lib.es5.d.ts? https://gist.github.com/betawaffle/98f10203a9d97eb43e64468488b3df9a

AnyhowStep

@AnyhowStep

The TS team tends to shy away from using generics and conditional types in the lib.d.ts files, from my experience

Andrew Hodges

@betawaffle

has anybody made a library with extensions like that to get more type information out?

another thing i'd like to see would be the ability to replace any with unknown in a lot of places

like maybe a compiler option to treat any the same as unknown?

Keith Layne

@keithlayne

I'd like that, it wouldn't break some things, but sadly there are places where you need any and unknown wouldn't work.

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