ESMitter

ESMitter (read: E-S-Emitter; a pun on ESM + emitter) is an event emitter compatible with Node.js, Deno and modern browsers. It is a fork of EventEmitter3, but natively TypeScript, ESM-only and with more modern tooling. The complete codebase has been converted to TypeScript and EcmaScript module syntax (ESM). ESMitter is currently less performant than EventEmitter3, but still fast with millions of operations per second.

Installation and Usage with Node.js

npm install --save esm-itter

After installation the only thing you need to do is import the module and use it as a parent class. One of the main features of ESMitter (beside being ESM-only) is that it is strongly typed, so you will need to provide type definitions for your events. Here is a simple example:

import { ESMitter, type ESMitterEvent } from "esm-itter";

class MyClass extends ESMitter<{
  success: ESMitterEvent<[{ foo: string; bar: string }]>;
  error: ESMitterEvent<[number, string]>;
}> {}

const instance = new MyClass();

// Attach event listener
instance.on("success", ({ foo, bar }) => {
  /* [...] */
});

Installation and Usage with Deno + JSR

deno add jsr:@tillsanders/esm-itter

After installation the only thing you need to do is import the module and use it as a parent class. One of the main features of ESMitter (beside being ESM-only) is that it is strongly typed, so you will need to provide type definitions for your events. Here is a simple example:

import { ESMitter, type ESMitterEvent } from "@tillsanders/esm-itter";

class MyClass extends ESMitter<{
  success: ESMitterEvent<[{ foo: string; bar: string }]>;
  error: ESMitterEvent<[number, string]>;
}> {}

const instance = new MyClass();

// Attach event listener
instance.on("success", ({ foo, bar }) => {
  /* [...] */
});

Tests and benchmarks

This module is well tested. You can run:

• npm test to run the tests under Node.js.
• npm run coverage to run the tests and generate a coverage report.

We also have a set of benchmarks to compare EventEmitter3 with some available alternatives. To run the benchmarks run npm run benchmark.

Tests and benchmarks are not included in the npm package. If you want to play with them you have to clone the GitHub repository. Note that you will have to run an additional npm i in the benchmarks folder before npm run benchmark.

Known incompatibilities with EventEmitter3

• The listenerCount() method requires an event name as the first argument and will thus not return the number of listeners for all events combined.

Status

This library has been tested using unit tests and has achieved excellent code coverage. It is being used in production and is considered stable. Contributions are welcome to improve any aspect of the library, including performance, documentation, and features.

License & Authors

This module is licensed under MIT.

It is a fork of the wonderful EventEmitter3 by Arnout Kazemier and has been converted to TypeScript and ESM by Till Sanders. For ES3 and CommonJS support, as well as superior performance, please use EventEmitter3.