[bug?] Cannot find name 'EventEmitter', property 'channel' of exported interface has or is using private name 'EventEmitter'.

TypeScript Version: 3.3.0-dev.20181129

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The search results led to issues like this one: #6307

Code

// ./Events.ts
class EventTypes {
  constructor(
    public SOME_EVENT: any,
    public OTHER_EVENT: any,
  ) {}
}

export const Events = {} as { [k in keyof EventTypes]: k }

for (const key in new (EventTypes as any)) {
    Events[key] = key
}

import * as events from 'events' // definitions are from `@types/node`

// our own (better, more type-safe) definition of EventEmitter
interface BetterEventEmitter<EventTypes> {
  new(): BetterEventEmitter<EventTypes>
  addListener<EventName extends keyof EventTypes> (event: EventName, listener: (arg: EventTypes[EventName]) => void);
  on<EventName extends keyof EventTypes> (event: EventName, listener: (arg: EventTypes[EventName]) => void);
  once<EventName extends keyof EventTypes> (event: EventName, listener: (arg: EventTypes[EventName]) => void);
  removeListener<EventName extends keyof EventTypes> (event: EventName, listener: (arg: EventTypes[EventName]) => void);
  removeAllListeners<EventName extends keyof EventTypes>(event?: EventName): this;
  emit<EventName extends keyof EventTypes>(event: EventName, arg: EventTypes[EventName]): boolean;
  eventNames<EventName extends keyof EventTypes>(): Array<EventName>;
  setMaxListeners(n: number): this;
  getMaxListeners(): number;
  listeners<EventName extends keyof EventTypes>(event: EventName): (arg: EventTypes[EventName]) => void[];
  listenerCount<EventName extends keyof EventTypes>(type: EventName): number;
  prependListener<EventName extends keyof EventTypes>(event: EventName, listener: (arg: EventTypes[EventName]) => void): this;
  prependOnceListener<EventName extends keyof EventTypes>(event: EventName, listener: (arg: EventTypes[EventName]) => void): this;
}

// override Node EventEmitter with our definition
export const EventEmitter = events.EventEmitter as unknown as BetterEventEmitter<EventTypes>

// consumer.ts
import { Events, EventEmitter } from './models/Events' // ERROR: `EventEmitter` is declared but its value is never read.

const channel = new EventEmitter // works fine, no error!

class Foo {
  channel: EventEmitter // ERROR, Cannot find name 'EventEmitter'
}

export interface Bar {
  channel: EventEmitter // ERROR, Cannot find name 'EventEmitter', property 'channel' of exported interface has or is using private name 'EventEmitter'.
}

Expected behavior:

I expect not to get the ERRORs I've marked in the above comments.

Actual behavior:

I'm getting those errors.

Playground Link:

I can't put multiple files in Playground or install dependencies.

Related Issues:

#6307

(My tsconfig includes "declaration": true)

You

export const EventEmitter

but you also need to export a type named EventEmitter if you want to reference one as such.

Ah I see, yep it works. It's not so intuitive though. Isn't it obvious that I'm exporting a constructor (therefore a type)? Seems like the compiler should be able to pick that up.

I'll close this though, as that's indeed how to make it work, but curious what you think about the compiler being able to detect that I'm exporting a constructor (and therefore a type).

This declaration stuff is funky. I'm on typescript 3.3.0-dev.20181129.

Now that I fixed that problem by adding the export of the type, not just the runtime value, I now have an error in another file:

Parameter 'channel' of constructor from exported class has or is using name 'BetterEventEmitter' from external module "/path/to/Events.ts" but cannot be named.

on some code that looks like

import { Events, EventEmitter } from '../models/Events'

export abstract class Foo {
  protected constructor(
    readonly channel?: EventEmitter, // ERROR here
  ) {
    // ...
  }
  // ...
}

Here's a screenshot:

Looks like maybe #9944 is not fixed.

However, this only happens to me in one file, but I can't reproduce it in another file. So something is weird here.

I was able to fix the previous comment's error by changing

interface BetterEventEmitter<EventTypes> {

to

export interface BetterEventEmitter<EventTypes> {

but I shouldn't have to do that, I'm not importing that name anywhere, it is only ever used in the definition of what EventEmitter is.

Looks like that "declaration": true, feature is not working as expected.

Use export { BetterEventEmitter as EventEmitter } instead of export type EventEmitter = BetterEventEmitter - the first establishes a usable alias, while due to some design limitations, the second isn't something we usually can locate for declaration emit.

It's hard to understand why, as with my eyes I can locate it just fine. Thanks for that tip!

This issue has been marked as 'Question' and has seen no recent activity. It has been automatically closed for house-keeping purposes. If you're still waiting on a response, questions are usually better suited to stackoverflow.

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[bug?] Cannot find name 'EventEmitter', property 'channel' of exported interface has or is using private name 'EventEmitter'. #28754

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[bug?] Cannot find name 'EventEmitter', property 'channel' of exported interface has or is using private name 'EventEmitter'. #28754

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trusktr commented on Nov 30, 2018

weswigham commented on Nov 30, 2018

trusktr commented on Dec 1, 2018

trusktr commented on Dec 1, 2018

trusktr commented on Dec 3, 2018

trusktr commented on Dec 3, 2018

weswigham commented on Dec 3, 2018

trusktr commented on Dec 14, 2018

typescript-bot commented on Jul 13, 2019

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