typed-emitter

library2.1.0jsnpmunverified

Typed-emitter is a lightweight TypeScript-only package (zero runtime bytes) that provides a strictly typed interface for event emitters. It is currently stable at version 2.1.0, receiving minor updates for bug fixes and feature enhancements, with occasional breaking changes primarily around type constraints or specific integration points like RxJS. Unlike `@types/node` which offers loose typings, or `eventemitter3` which lacks strong argument typing, typed-emitter allows developers to define a precise `EventMap` for their emitter instances. This enables compile-time verification of event names and listener argument signatures, preventing common runtime errors. It's designed to be used with existing `EventEmitter` implementations, such as Node.js's built-in `events` module or browser-based alternatives, without providing its own implementation.

type-stubs

npm install typed-emitter

github ↗package ↗

INSTALL

IMPORT

SIG · TYPED-EMITTER

typed-emitter

type-stubsjavascriptv2.1.0

Install

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Import

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Disk

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Pass rate

0/ 6

Env Coverage0 / 6

glibc

18–22

musl

18–22

Install & Compatibility

Where this runs

tested against v? · npm install

Install × environment matrix

Each cell = how many times install + import succeeded across repeated harness runs. Partial = flaky.
glibc = Debian/Ubuntu slim · musl = Alpine Linux

musl

node 18–226 runs

build_error

glibc

node 18–226 runs

build_error

Code

Verified usage

Verified import paths — ran on the pinned version, not inferred.

TypedEmitter

✓ import TypedEmitter from 'typed-emitter'

✗ import { TypedEmitter } from 'typed-emitter'

TypedEmitter is a default export.

FromEvent

✓ import { FromEvent } from 'typed-emitter/rxjs'

✗ import { FromEvent } from 'typed-emitter'

The FromEvent interface for RxJS compatibility is exported from a subpath.

Arguments

✓ import { Arguments } from 'typed-emitter'

✗ import Arguments from 'typed-emitter'

Arguments is a named type export, useful for extracting listener parameter types.

Demonstrates defining event map types and applying them to a standard Node.js EventEmitter, showcasing compile-time type checking for `emit` and `on` calls.

import EventEmitter from "events"; import TypedEmitter from "typed-emitter"; type MessageEvents = { error: (error: Error) => void; message: (body: string, from: string) => void; statusUpdate: (status: 'online' | 'offline') => void; }; const messageEmitter = new EventEmitter() as TypedEmitter<MessageEvents>; // Good: TypeScript validates event name and argument types messageEmitter.emit("message", "Hi there!", "no-reply@test.com"); messageEmitter.emit("statusUpdate", "online"); // TypeScript will catch type mistakes // @ts-expect-error Argument of type 'boolean' is not assignable to parameter of type 'string'. messageEmitter.emit("message", "Hi there!", true); // @ts-expect-error Argument of type 'string' is not assignable to parameter of type '"online" | "offline"'. messageEmitter.emit("statusUpdate", "connecting"); // Good: Type-safe listener registration messageEmitter.on("error", (error: Error) => { console.error(error.message); }); // TypeScript will catch mistakes in listener signatures // @ts-expect-error Argument of type 'string' is not assignable to parameter of type 'Error'. messageEmitter.on("error", (error: string) => { /* ... */ }); console.log('Typed emitter setup successfully.'); // To prevent process from exiting immediately in Node.js setInterval(() => {}, 1000);

Debug

Known issues

breakingSince v2.0.0, the `TypedEmitter` generic type parameter `Events` is strictly constrained to `EventMap` (`{ [key: string]: (...args: any[]) => void }`). Your event map types must conform to this structure, where all properties are functions.

fix

Ensure all properties within your `EventMap` type are defined as functions (e.g., `(arg1: Type, arg2: Type) => void`).

affects: >=2.0.0

breakingWith v2.1.0, a new `TypedEmitter` interface for RxJS compatibility was introduced, exported from `typed-emitter/rxjs`. If you were previously using custom workarounds or older patterns for RxJS `fromEvent` type inference, you may need to update your imports and usage to leverage the new `FromEvent` type.

fix

Import `FromEvent` from `typed-emitter/rxjs` and cast `rxjs.fromEvent` to it: `import { fromEvent as rxFromEvent } from "rxjs"; import { FromEvent } from "typed-emitter/rxjs"; const fromEvent = rxFromEvent as FromEvent;`

affects: >=2.1.0

gotchaPrior to v1.4.0, the `package.json` `main` field incorrectly pointed to a TypeScript `.ts` file instead of the compiled JavaScript. While fixed in v1.4.0, older versions might cause resolution issues, build failures, or unexpected behavior in bundlers or environments that don't correctly process `.ts` files directly as a main entry point.

fix

Upgrade to `typed-emitter` v1.4.0 or newer to ensure correct package resolution and avoid potential build issues.

affects: <1.4.0

Errors

Common errors & fixes

Argument of type 'string' is not assignable to parameter of type 'Error'.

An event listener function's parameter type does not match the type defined in the `EventMap` for that event.

fix

Adjust the listener function signature (parameter types) to precisely match the `EventMap` definition for the corresponding event.

Property 'myUndefinedEvent' does not exist on type 'TypedEmitter<MyEventMap>'.

Attempting to emit or listen to an event name that has not been explicitly defined in the `EventMap` provided to `TypedEmitter`.

fix

Add the desired event name and its corresponding listener signature to your `EventMap` type definition.

Type 'MyCustomEventMap' does not satisfy the constraint '{ [key: string]: (...args: any[]) => void; }'. Type 'MyCustomEventMap' is not assignable to type '{ [key: string]: (...args: any[]) => void; }'. Property 'invalidKey' is incompatible with index signature. Type 'string' is not assignable to type '(...args: any[]) => void'.

Your custom event map type contains properties that are not functions, violating the `EventMap` constraint introduced in v2.0.0.

fix

Ensure that every property (event name) in your `EventMap` is defined as a function type (e.g., `eventName: (arg1: Type) => void`).

Upgrade

Version history

2.1.0latest on npm

Audit

Dependencies

No dependency data recorded yet.

Agent activity

20 hits · last 30 days

node

OpenAI (training)

Resources

githubhttps://github.com/andywer/typed-emitter ↗

packagehttps://www.npmjs.com/package/typed-emitter ↗