@types/typescript does not work with import syntax

[dalcde]

Reproduce by running the following in an empty directory:

npm init
npm i yargs
echo "import yargs from 'yargs';" > index.ts
tsc index.ts

We get the error

index.ts:1:19 - error TS2307: Cannot find module 'yargs' or its corresponding type declarations.

1 import yargs from 'yargs'
                    ~~~~~~~


Found 1 error.

Reproduced with yargs 16.0.3 and tsc 4.0.2.

[AviVahl]

https://github.com/yargs/yargs#typescript
yargs doesn't ship built-in types yet, so one has to install @types/yargs as well.

[dalcde]

This worked with yargs 15.4.2

[AviVahl]

Maintainers are working to convert the entire project to TypeScript: #1586
Work there is probably related. They do write about @types/yargs and the built-in .d.ts

[bcoe]

I apologize for the confusion it created having this briefly work in v15. We do not intend to ship TypeScript definitions in yargs or yargs-parser in the near future.

Here's a post on the topic.

@types/yargs is well supported and used widely by the community, but deviates sigificantly from the actual TypeScript API surface of the library.

Basically, we had the choice break TypeScript for 1000s of existing libraries, or ship without types ourselves... I think this is the right call.

The other problem with shipping the library itself with the types is that breaking changes to types vs the API surface become indistinguishable.

[dalcde]

I understand that pure javascript libraries can be used in typescript projects (as in they can be imported and used, but not type checked), and I assumed that's how it previously worked. Currently it can't be imported at all.

[bcoe]

@dalcde the syntax should be:

#!/usr/bin/env node
import yargs = require('yargs');

const argv = yargs.options({
  a: { type: 'boolean', default: false },
  b: { type: 'string', demandOption: true },
  c: { type: 'number', alias: 'chill' },
  d: { type: 'array' },
  e: { type: 'count' },
  f: { choices: ['1', '2', '3'] }
}).argv;

I believe to match the @types/yargs definitions.

[bcoe]

@dalcde I wonder if, now that we support ESM in yargs, there's a way @types/yargs could be modified to support both require and import syntax.

The reason that = require('yargs'); is necessary, is because the non-ESM API surface of yargs uses module.exports.

[AviVahl]

@bcoe you can already import yargs as 'yargs'; if you have esModuleInterop turned on (default in tsc --init) and @types/yargs in place.
We do so in stylable: https://github.com/wix/stylable/blob/master/packages/cli/src/cli.ts

We are getting yargs in its require form though, as our modules transpile to commonjs (meaning a require('yargs') is being called).

EDIT: just to clarify... esModuleInterop causes allowSyntheticDefaultImports to be turned on, which causes the type checker to allow importing "commonjs modules" (.d.ts says export =) using default import.

[bcoe]

@AviVahl, I wish this was a bit more straightforward for folks ... especially now that the library itself does support ESM. I think there's just room to improve the ESM/TypeScript interop story.

[bcoe]

@dalcde if @AviVahl's approach works for you, perhaps we can close this?

[dalcde]

I get the same error with --esModuleInterop

[bcoe]

@dalcde could you share a minimal repository that is having this issue?

[dalcde]

The commands at the OP of the issue creates such a repository.

[AviVahl]

Those commands do not include @types/yargs, so you'll get a type error.
Also, they do not include npx tsc --init, so no tsconfig.json was created, and you may be missing other important config (module/moduleResolution)

mkdir yargs-ts-test
cd yargs-ts-test/
npm init -y
npm i yargs
npm i @types/yargs typescript -D
npx tsc --init
echo "import yargs from 'yargs';" > index.ts
npx tsc index.ts 

Works just fine (notice the added npm i @types/yargs typescript -D and npx tsc --init).

[dalcde]

I can confirm that adding `@types/yargs` solves the problem. `tsc --init` does not. The issue was that javascript libraries are normally usable with typescript without typings, and that was the case with yargs prior to 16.0