Typed-Emitter
![NPM Version](https://img.shields.io/npm/v/typed-emitter.svg)
Strictly typed event emitter interface for TypeScript.
Code size: Zero bytes - Just the typings, no implementation. Use the default event emitter of the events
module in node.js or bring your favorite implementation when writing code for the browser.
Installation
$ npm install --save-dev typed-emitter
$ yarn add --dev typed-emitter
Usage
import EventEmitter from "events"
import TypedEmitter from "typed-emitter"
interface MessageEvents {
error: (error: Error) => void,
message: (body: string, from: string) => void
}
const messageEmitter = new EventEmitter() as TypedEmitter<MessageEvents>
messageEmitter.emit("message", "Hi there!", "no-reply@test.com")
messageEmitter.emit("mail", "Hi there!", "no-reply@test.com")
messageEmitter.emit("message", "Hi there!", true)
messageEmitter.on("error", (error: Error) => { })
messageEmitter.on("error", (error: string) => { })
messageEmitter.on("failure", (error: Error) => { })
Extending an emitter
You might find yourself in a situation where you need to extend an event emitter, but also want to strictly type its events. Here is how to.
class MyEventEmitter extends (EventEmitter as new () => TypedEmitter<MyEvents>) {
}
As a generic class:
class MyEventEmitter<T> extends (EventEmitter as { new<T>(): TypedEmitter<T> })<T> {
}
Why another package?
The interface that comes with @types/node
is not type-safe at all. It does not even offer a way of specifying the events that the emitter will emit...
The eventemitter3
package is a popular event emitter implementation that comes with TypeScript types out of the box. Unfortunately there is no way to declare the event arguments that the listeners have to expect.
There were a few other examples of type-safe event emitter interfaces out there as well. They were either not published to npm, had an inconsistent interface or other limitations.
License
MIT