Provide Typescript type declarations for jco API

[landonxjames]

I am attempting to use jco as a library from a Typescript project. The following import throws an error:

import { transpile } from "@bytecodealliance/jco";

Throws:

Could not find a declaration file for module '@bytecodealliance/jco'. '/Volumes/workplace/project/node_modules/@bytecodealliance/jco/src/api.js' implicitly has an 'any' type.
  Try `npm i --save-dev @types/bytecodealliance__jco` if it exists or add a new declaration (.d.ts) file containing `declare module '@bytecodealliance/jco';`ts(7016)

This appears to be because there are no .d.ts files in node_modules/@bytecodealliance/jco, so ts doesn't recognize the package. I can add my own declaration file to get unblocked, but this seems like a thing that will impact multiple users going forward.

From some quick research it seems like this could be handled in a few ways:

• Change jco to a typescript project, run tsc as part of the build to generate the .d.ts bindings
• Manually write ts bindings and distribute them with the package
• Manually write the bindings and contribute them to DefinitelyTyped

The first option looks like the best, but would be fairly disruptive. The other options might be quicker.

[landonxjames]

Happy to contribute to some work here, but would like feedback from project maintainers on what direction is preferable before I dive too far in.

[guybedford]

Thanks for bringing this up, we should definitely resolve it!

The file in src/api.js directly reexports from files that are all themselves typed, so it should be possible to achieve this with just an api.d.ts or jsdoc comments that reexport from the same interfaces.

So it should be a relatively PR to fix, and we shouldn't need to maintain much more than just those reexport declarations.

If you're able to look into this further that would be a huge help.

[landonxjames]

Almost done with this, but I'm encountering an error that I've encountered in my own projects as well. The file obj/wasm-tools.js referenced by the JSDoc types contains the following:

export { tools, tools as 'local:wasm-tools/tools' }

This is valid javascript, but (seemingly) not valid typescript. Ts accepts as fooBar, but not as "fooBar". This is probably a ts bug since it should mirror the js implementation.

In my own projects I've been handling this by seding in a replacement before running tsc, but that feels a but hacky for the project that generates those export statements. It should work here though as nothing appears to be using that alias.

Created a bug in the ts repo to track this: microsoft/TypeScript#56375

[landonxjames]

Ahh turns out this is already a known ts bug, but the fix for it seems to have stalled out: microsoft/TypeScript#40594

[guybedford]

Yes, for TypeScript definitions, we just have to omit these export names for now.