Better TypeScript support

[mohsen1]

💬 RFC Better TypeScript support

TypeScript is working out of the box for the most part but there are a few pain points:

Pain points

• TypeScript module resolution algorithm is not implemented in Parcel. [TypeScript] baseUrl inside tsconfig.json not supporting. #202 This covers these configs:
  • baseUrl
  • paths
  • allowSyntheticDefaultImports
• Compiler errors are not printed in the console 🐛 Not displaying or honoring Typescript errors #465
  • parcel-plugin-typescript adds it but console is not cleared after issue is resolved

Improvements

• Automatically create and configure tsconfig
  • Once a ts or tsx file was imported but tsconfig is not present, create one
• Automatically install @types packages Automatically install Typescript types #1161
• Support for Custom Typescript transformers Support for Custom Typescript transformers #699

🔦 Context

TypeScript is pretty popular and having first class support for it in Parcel will attract a wider range of users.

💻 Examples

I tried cloning react-parcel-example and making repo states that demonstrate those pain points:

1. JSX is not working in default mode (preserve):
   • https://github.com/mohsen1/react-parcel-example-typescript/tree/90f9f72b2f3fcfcbd5410b097e5c20cc10d8a325
2. baseUrl config is not working
   • https://github.com/mohsen1/react-parcel-example-typescript/tree/3b74951e47d77d7ba79dbd56ef25621d312ca394

[fathyb]

Duplicates :

• module resolution [TypeScript] baseUrl inside tsconfig.json not supporting. #202
• type checking 🐛 Not displaying or honoring Typescript errors #465
• auto install @types Automatically install Typescript types #1161

---

parcel-plugin-typescript implements the TypeScript module resolution (baseUrl, paths). allowSyntheticDefaultImports is not part of the module resolution algorithm, it's used for the module symbol resolution by the type-checker. If you are using TypeScript 2.8+ you should be able to import synthetic defaults.

The plugin is originally a spin-off of a PR implementing type-checking, but the feature wasn't well received by the community, so I guess it's better to leave the choice to the end user.

The TypeScript plugin will probably be integrated as a core plugin once we settle on a plugin RFC though (aka 2.0). The long term goal would be to integrate TypeScript just like we do with Babel, and let developers use a pure TypeScript toolchain with or without Babel.

[DeMoorJasper]

This will probably automatically happen once the new plugin system lands and we split up every plugin in a seperate package. Using parcel-plugin-ts as the default in that case. This will be part of the Parcel v2.0 update

[szagi3891]

@DeMoorJasper - When could this happen?

[DeMoorJasper]

Please use the +1 button instead of adding comments saying +1

[mihailik]

1627 Support <script src="tsconfig.json"></script> as asset type might be a way to solve many of those issues.

Rather than stretch parcel's file-based current TS handling, allow a way to fall back into TS standard way, using tsconfig.json directly.

That way all the resolution, errors, special modes will reside in TS compiler, and act in familiar TS manner.

[quantuminformation]

This best loaders use native typescript as much as possible.

[inad9300]

Wow, this seems to have been completely abandoned. Despite TypeScript's increase in popularity. Still no type checks.

[mischnic]

We are working on this for Parcel 2.

[tgroutars]

@mischnic Awesome, is there an issue we can follow for updates on parcel 2?

[mihailik]

@tgroutars comment above refers to Parcel 2/TypeScript transformer:

Mind you, that PR is old and not handling type checks (yet?)

[mischnic]

The current PR is #3083 (but doesn't have type checking either)

[DeMoorJasper]

Some initial work on typechecking: see #3142

[nexussays]

I posted a workaround for type errors in the console in a comment in #465 that others might find useful: #465 (comment)

I'm cross-posting because there are several issues on this topic and I'm not actually sure where I arrived from google; so this will hopefully save everyone else some time going through GitHub issues.

[bbugh]

I created an issue for Parcel 2 about the incomplete TypeScript support, and the official response by @DeMoorJasper is that Parcel 2 will effectively behave the same as Parcel 1 by stripping out TypeScript and treating it as JavaScript with babel. TypeScript code will not be compiled, so there will be no type checking or compiler errors. If you have a desire for real TypeScript support in Parcel 2, please comment in the new RFC: #4022

[devongovett]

Going to close this. Parcel 2 now does support loading setting from tsconfig.json and respects baseUrl, paths, etc. Type checking is not supported, but could be implemented in a third party plugin.