Does the world need another event dispatcher library?

Most event dispatchers are O(N). Fast Observer is a lightweight O(1) and asynchronous library. This is useful when:

• Performance matters (think mouse events or requestAnimationFrame())
• You want to work with async/await on publishing
• You care about file size
• Convenience features such as namespaces aren't necessary
• Works in the browser, on the server, and when doing SSR

Some extra tidbits:

• There are zero-dependencies
• It's well tested with benchmarks @see Performance

npm i --save fast-observer

It's unnecessary to profile the publishFast method. It's going to be as fast as calling a function directly.

However, the O(N) publish() method is 14.5 times faster the most popular event dispatcher library called PubSub-js.

• fast-observer: Executed 10000000 times in 436 ms
• PubSub-js: Executed 10000000 times in 6341 ms

See benchmarks here. I'd be happy to adjust or add more benchmarks if requested.

import Observer from "fast-observer";

const o = new Observer();

// Define some O(N) subscriptions (nothing new here).
o.subscribe("launch ship", launchTheShip);
o.subscribe("launch ship", launchTheOtherShip);
o.subscribe("launch ship", launchTheOtherShip);

await o.publish("launch ship"); // Wait for all the ships to launch.

// Define O(1) subscription.
o.subscribeFast("engine propulsion", handlePropulsion);

await o.publishFast("engine propulsion"); // Similar to publish, is a promise.

The major caveat of subscribeFast is that there can only be one. If there are multiple, they will override each other. There's no magic here - subscribeFast and publishFast is just more of structured way to call a function.

• subscribe(eventName: string, (payload?: any) => void | Promise<void>): void
• unsubscribe(eventName: string, fn): void
• subscribeFast(eventName: string, (payload?: any) => void | Promise<void>): void
• unsubscribeFast(eventName: string): void
• publish(eventName: string): Promise<void>
• publishFast(eventName: string): Promise<void>

1. npm i && tsc -w to install dev-deps & watch
2. npm test to run tests

Apache Version 2.0

See LICENSE