Expose ~JSX namespace~ `HResult` globally

[alecmev]

Initial checklist

• I read the support docs
• I read the contributing guide
• I agree to follow the code of conduct
• I searched issues and couldn’t find anything (or linked relevant results below)

Problem

I'm using TypeScript with "moduleResolution": "Node16" and JSX, and I want to have explicit return types. Currently I do this:

import type { Root, Element } from "hast";
const Foo = (): Root | Element => <div />;

Instead, I'd like to be able to do this:

const Foo = (): JSX.Element => <div />;

I know it's an alias of HResult, which can be imported from lib/core, but it isn't idiomatic, and lib/core currently isn't exposed, so it doesn't work in this module resolution mode.

Solution

@types/react puts JSX in declare global. Could hastscript do that too?

Alternatives

Export lib/core.

[wooorm]

Sounds like something @remcohaszing has ideas on!

[remcohaszing]

The node16 resolution type is the correct one for native ESM, and therefor for unified packages internally. Unfortunately not all of the ecosystem is compatible yet (davidbonnet/astring#646). This needs to be resolved first, then I can look at how all of this affects hastscript.

A quick history on this topic:

• At first the TypeScript JSX namespace had to be global.

  declare global {
    namespace JSX {
      // …
    }
  }

  During this time the React types were created.
• At some point TypeScript allowed specifying local JSX namespaces

  declare function h();
  
  namespace h.JSX {
    // …
  }

  This allows people to mix multiple JSX implementations in different filed within the same project 🤯 So these two files could live in the same project:
  // react-hello.tsx

  import React from 'react'
  
  const Hello = () => <div>Hello</div>

  // hastscript-hello.tsx

  /* @jsx h */
  import { h } from 'hastscript'
  
  const Hello = () => <div>Hello</div>

• Then the automatic runtime was released.

As far as I know, this requires a global JSX namespace. However, this issue suggests this is incorrect. If this is indeed incorrect, then IMO it is the desired behaviour, because it would allow to mix multiple JSX implementationg using JSX comments.

I do think it would be nice to expose the HResult type though. I totally agree it makes sense to use this type, i.e. for explicit return types as the OP suggests.

import { HResult } from 'hastscript'

const Foo = (): HResult => <div />;

[alecmev]

Thanks, that makes sense! So I went ahead and checked if anybody has reported this in TypeScript, since this feels like their responsibility, and I found something even better: microsoft/TypeScript#41330 (comment) Here's how Preact implemented it: https://github.com/preactjs/preact/pull/2811/files Edit: And I see that it's already exported, so why doesn't it work? Edit 2: Ah, likely because it isn't re-exported here and here and here. Edit 3: No, I still don't understand why this isn't sufficient:

// svg/jsx-runtime.d.ts

export * from '../lib/runtime-svg.js'

// lib/runtime-svg.d.ts

export * from './jsx-automatic.js'

// lib/jsx-automatic.d.ts

export namespace JSX ...

Edit 4: Okay, finally found the definitive answer to this: microsoft/TypeScript#47072 (comment) The JSX namespace is an implementation detail, not meant to be public. So, in the end, import { HResult } is the way to go.

[wooorm]

As far as I understand the above comments, then it would be bad to do this?
And exposing HResult is an adequate solution?

[alecmev]

it would be bad to do this?

Yep! Looks like JSX isn't meant to be accessed ever.

exposing HResult is an adequate solution?

I believe so. The name is a little cryptic, but it's not worth a refactor, and breaking existing consumers.

[wooorm]

I’m up for exposing HResult, I don’t see downsides.
@alecmev Interested in working on a PR?

[github-actions]

Hi! This was marked as ready to be worked on! Note that while this is ready to be worked on, nothing is said about priority: it may take a while for this to be solved.

Is this something you can and want to work on?

Team: please use the area/* (to describe the scope of the change), platform/* (if this is related to a specific one), and semver/* and type/* labels to annotate this. If this is first-timers friendly, add good first issue and if this could use help, add help wanted.