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README.md

💧EventEmitter's typesafe replacement💧


'evt' is intended to be a replacement for 'events'.
It enables and encourages functional programming and makes heavy use of typescript's type inference features to provide type safety while keeping things concise and elegant 🍸.

Suitable for any JS runtime env (deno, node, old browsers, react-native ...)

  • It is both a Deno and an NPM module. ( Achieved with Denoify )
  • Lightweight, no dependency.
  • No polyfills needed, the NPM module is transpiled down to ES3
  • React Hooks integration

Can be imported in TypeScript projects using version >= 3.4 (Mar 2019) and in any plain JS projects.

TL;DR*

import { Evt } from "evt";

const evtText = new Evt<string>();
const evtTime = new Evt<number>();

evtText.attach(text => console.log(text));
evtTime.attachOnce(time => console.log(time));

evtText.post("hi!"); //Prints "hi!"
evtTime.post(123);   //Prints "123"
evtTime.post(1234);  //Prints nothing

OR

import { Evt, to } from "evt";

const evt = new Evt<
    [ "text",  string ] | 
    [ "time",  number ]
>();

//Mind the '$' prefixing 'attach'
evt.$attach(to("text"), text => console.log(text));
evt.$attachOnce(to("time"), time => console.log(time));

evt.post(["text", "hi!"]);
evt.post(["time", 123]);
evt.post(["time", 1234]);

*Those are introductory examples, EVT can do much more than this.

Who is using it


Install / Import

In Deno:

import { Evt } from "https://deno.land/x/evt/mod.ts";

Anywhere else:

$ npm install --save evt
import { Evt } from "evt"; 

Import from HTML, with CDN

<script src="//unpkg.com/evt/bundle.min.js"></script>
<script>
    const { Evt } = window["evt"];
</script>

Try it

Run some examples

Motivations

There are a lot of things that can't easily be done with EventEmitter:

  • Enforcing type safety.
  • Removing a particular listener ( if the callback is an anonymous function ).
  • Adding a one-time listener for the next event that meets a condition.
  • Waiting (via a Promise) for one thing or another to happen.
    Example: waiting at most one second for the next message, stop waiting if the socket disconnects.

Why would someone pick EVT over RxJS:

  • RxJS introduces a lot of abstractions. It's a big jump from EventEmitter.
  • With RxJS It is often needed to resort to custom type guards, the filter operator breaks the type inference.
  • RxJS tends to be quite verbose.
  • It could be months before RxJS it eventually supports Deno.
  • No official guideline on how to integrate RxJS with React.

EVT is an attempt to address all these points while trying to remain as accessible as EventEmitter.


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