`web-features` doesn't export types gracefully

[SachaG]

Is there a way to import the type definition for a Web Feature object?

[ddbeck]

Ah, this is a bit of a known issue. Exporting types are a little broken (though there is a types file).

They were originally added to the package in #540, but #1542 noted that they're somewhat awkward to work with. You can see that (abandoned) PR for a workaround.

We ought to properly fix this though, so it's possible to do something more natural like import type { … } from "web-features".

[Jym77]

It also seems that the syntax currently used in types.d.ts in the package breaks when using ESM rather than CJS modules.

import("./types").FeatureData gives a "Relative import paths need explicit file extensions in ECMAScript imports when '--moduleResolution' is 'node16' or 'nodenext'." error, and should be replaced by import("./types.d.ts").FeatureData to get ESM projects working.

(workaround: skipLibCheck, but it's quite heavy-handed)

[ddbeck]

@Jym77 Thanks for reporting this. Is it possible you could provide a minimal reproduction of the error? I couldn't get this to happen myself, so I figure I've got the wrong combination of source, tsconfig, and runtime. Reproduction steps (or at least a tsconfig) would be quite helpful.

I've opened #3589, which I think resolves all of the problems noted in this issue, but I'm reluctant to ask for a review and merge without more confidence that it will fix the problems.

[Jym77]

@ddbeck MNWE repo, Failing build in action.

package.json:

  "type": "module",
  "packageManager": "yarn@4.12.0",
  "devDependencies": {
    "@types/node": "^24.10.0",
    "typescript": "^5.9.3"
  },
  "dependencies": {
    "web-features": "^3.9.3"
  }

tsconfig.json:

{
  "compilerOptions": {
    "module": "nodenext",
    "target": "esnext",
    "skipLibCheck": false
  },
  "files": [
    "./src/web-features.ts"
  ]
}

source file:

import { features } from "web-features";

console.log(features);

yarn tsc --build output:

Error: node_modules/web-features/index.d.ts(1,32): error TS2307: Cannot find module './types.quicktype' or its corresponding type declarations.
Error: node_modules/web-features/index.d.ts(2,27): error TS2834: Relative import paths need explicit file extensions in ECMAScript imports when '--moduleResolution' is 'node16' or 'nodenext'. Consider adding an extension to the import path.
Error: node_modules/web-features/index.d.ts(2,59): error TS2834: Relative import paths need explicit file extensions in ECMAScript imports when '--moduleResolution' is 'node16' or 'nodenext'. Consider adding an extension to the import path.
Error: node_modules/web-features/index.d.ts(2,96): error TS2834: Relative import paths need explicit file extensions in ECMAScript imports when '--moduleResolution' is 'node16' or 'nodenext'. Consider adding an extension to the import path.
Error: node_modules/web-features/index.d.ts(4,27): error TS2307: Cannot find module './types.quicktype' or its corresponding type declarations.
Error: node_modules/web-features/index.d.ts(6,27): error TS2307: Cannot find module './types.quicktype' or its corresponding type declarations.
Error: Process completed with exit code 1.

[Jym77]

This seems to be linked to the nodenext/esnext options in TSconfig as removing them clears the problem.

[ddbeck]

@Jym77 thank you, that's extremely helpful! Using a build from #3589 fixes your example repo. I've included you as a co-author on the commit, since that was the hard part.

I'm going to make sure it plays nice with some other type changes in happening in a more complex PR, so that I don't accidentally force myself to do a breaking change. As soon as I've done that (perhaps tomorrow), I'll ask for review on the bug fix. Thank you again!