Fails to generate typescript declarations from JS when extending EventEmitter

[vasco-santos]

Bug Report

🔎 Search Terms

• EventEmitter
• TS9006
• Declaration emit for this file requires using private name
• An explicit type annotation may unblock declaration emit

🕗 Version & Regression Information

• typescript@4.0.5
  • could not try this out with next versions as there are a few bugs already reported that will need to be fixed

This happened from 15th, more precisely after DefinitelyTyped/DefinitelyTyped#50266 being merged and released.

⏯ Playground Link

I believe I cannot add JS here 😞

You can look into libp2p before this PR being merged libp2p/js-libp2p#846.

Commit hash to use: d19401aa4cafcf2237af90b677c743b0ff0f871e. Just need npm i && npm run build

💻 Code

const { EventEmitter } = require('events')

class Manager extends EventEmitter {
  constructor () {
    super()
  }
}

module.exports = Manager

🙁 Actual behavior

Cannot generate typescript declaration file with errors like:

src/connection-manager/latency-monitor.js:2:1 - error TS9006: Declaration emit for this file requires using private name 'EventEmitter' from module '"events"'. An explicit type annotation may unblock declaration emit.

2  'use strict'

🙂 Expected behavior

Does not fail to build and generate the declaration files.

[RyanCavanaugh]

@weswigham seems WAI-ish, but is there anything more clever that could be done?

[weswigham]

Considering the TS equivalent,

import { EventEmitter } from 'events'

class Manager extends EventEmitter {
  constructor () {
    super()
  }
}

export = Manager

works fine, and that JS should be bound pretty similarly to the above TS now, I'm thinking it's probably a bug somewhere in JS declaration binding.

[ExE-Boss]

What happens if:

import internal = require('events');
namespace EventEmitter {
	// Should just be `export { EventEmitter }`, but that doesn't work in TypeScript 3.4
	export { internal as EventEmitter };
}

in @types/node/events.d.ts is changed into:

namespace EventEmitter {
	// Note that this only works from TypeScript 3.5 onwards:
	export { EventEmitter };
}

---

Also, I can’t reproduce this on TypeScript 4.1.

[weswigham]

Yeah, after looking at it, @ExE-Boss is right - this was fixed in 4.1. Check out the repro:

// @allowJs: true
// @checkJs: true
// @outDir: ./out
// @declaration: true
// @filename: node_modules/@types/node/index.d.ts
declare module "events" {
    import internal = require('events');
    class EventEmitter {
        member(): void;
    }
    namespace EventEmitter {
        // Should just be `export { EventEmitter }`, but that doesn't work in TypeScript 3.4
        export { internal as EventEmitter };
    }
    export = EventEmitter;
}

// @filename: file.js
/// <reference types="node" />

const { EventEmitter } = require('events')

class Manager extends EventEmitter {
  constructor () {
    super()
  }
}

module.exports = Manager

Workbench Repro

So, good news OP! It already works in 4.1 and above!