event-pubsub

What is event-pubsub?

The event-pubsub package is a Node.js module that provides a simple interface for implementing the publish-subscribe pattern. This pattern allows for the creation of a decoupled system where publishers and subscribers can communicate through events without being directly connected.

What are event-pubsub's main functionalities?

Event Emission

This feature allows you to emit events with a specified name and pass data to the event listeners. In the code sample, an event listener is set up to listen for the 'sayHello' event and emit that event with a parameter.

const EventPubSub = require('event-pubsub');
const events = new EventPubSub();

// Event listener
events.on('sayHello', name => console.log(`Hello, ${name}!`));

// Emit event
events.emit('sayHello', 'World');

Event Listening

This feature allows you to listen for events by name. When the event is emitted, the callback function is called with any data passed to the event. In the code sample, an event listener is set up to listen for the 'dataReceived' event.

const EventPubSub = require('event-pubsub');
const events = new EventPubSub();

// Event listener
events.on('dataReceived', data => console.log(`Data: ${data}`));

Once Listeners

This feature allows you to set up event listeners that will only be triggered once. After the event is emitted and the listener is invoked, the listener is removed. In the code sample, an event listener is set up to listen for the 'initialize' event and will only be triggered once.

const EventPubSub = require('event-pubsub');
const events = new EventPubSub();

// Event listener that fires once
events.once('initialize', () => console.log('Initialization complete.'));

Removing Listeners

This feature allows you to remove specific event listeners. In the code sample, an event listener is added and then removed for the 'message' event.

const EventPubSub = require('event-pubsub');
const events = new EventPubSub();

function onMessage(content) {
  console.log(`Message: ${content}`);
}

// Add and remove an event listener
events.on('message', onMessage);
events.off('message', onMessage);

Other packages similar to event-pubsub

eventemitter3

eventemitter3 is a high performance EventEmitter. It provides similar functionality to event-pubsub but focuses on performance and is compatible with different module systems (CommonJS, AMD, and browser globals).

mitt

mitt is a tiny functional event emitter / pubsub. It offers a similar publish-subscribe pattern but with a smaller footprint, making it a good choice for front-end development and projects where size is a concern.

wolfy87-eventemitter

wolfy87-eventemitter is an EventEmitter implementation that provides asynchronous event emitting and namespaced events. It is more feature-rich compared to event-pubsub, offering additional functionality such as context binding and wildcard events.

README

Event PubSub

npm install event-pubsub

npm info : See npm trends and stats for event-pubsub

GitHub info :

Build Info :
Travis CI (linux,windows & Mac) :

Super light and fast Extensible ES6+ event system for Node and the browser the same files that work in node will work in the browser without any modifications. If you must support old browsers you can transpile the module.

Methods

Method	Arguments	Description
on	type:string, handler:function, once:boolean	will bind the handler function to the the type event. Just like addEventListener in the browser. If once is set to true the hander will be removed after being called once.
once	type:string, handler:function	will bind the handler function to the the type event and unbind it after one execution. Just like addEventListener in the browser withe the once option set
off	type/*:string, handler/*:function	will unbind the handler function from the the type event. If the handler is *, all handlers for the event type will be removed. Just like removeEventListener in the browser, but also can remove all event handlers for the type.
emit	type:string, ...data arguments	will call all handler functions bound to the * event and the type event. It will pass all ...data arguments to those handlers, for * events, the first arg will be the type you can filter the events
reset		Removes all events of any and all types including *

Members

Member	Type	Description
.list	Object	List representation of all the bound events, primarily used for visibility.

The * event type

The * event type will be triggered by any emit. These also run first. The handlers for * should expect the first arg to be the type and all args after that to be data arguments.

Local website

npm start actually starts a node-http-server. So if you just want quick links to the example and test web pages, there is a page in the root of this module with links. You can access it by going to the local homepage : http://localhost:8000

Provided your router and firewall are not blocking your IP/ports, you can also go to http://[your-ip-here]:8000/ on any device including your mobile device provided it is on the same network.

Digital Ocean Static App

We use the free Digital Ocean Static Apps to host a version of the local server. It is exactly the same as if you ran npm start on your machine. You can also use this like a CDN as it automatically rebuilds from main/master each time the branch is updated. event-pubsub CDN home : https://cdn-p939v.ondigitalocean.app/event-pubsub/

Basic Examples

//relative paths will let your code work in both node and the browser without transpiling unless you want to.
import EventPubSub from './node_modules/event-pubsub/index.js';

events=new EventPubSub

events.on(
    'hello',
    (data)=>{
        console.log('hello event recieved ', data);
    }
);

events.emit(
    'hello',
    'world'
);

Basic Chaining

events.on(
    'hello',
    someFunction
).on(
    'goodbye',
    anotherFunction
).emit(
    'hello',
    'world'
);

events.emit(
    'goodbye',
    'humans'
).off(
    'hello',
    '*'
);

Basic Event Emitter and/or Extending Event PubSub

//relative paths will let your code work in both node and the browser!
import EventPubSub from './node_modules/event-pubsub/index.js';


class Book extends EventPubSub{
    constructor(){
        super();
        //now Book has .on, .off, and .emit

        this.words=[];
    }

    add(...words){
        this.words.push(...words);
        this.emit(
            'added',
            ...words
        );
    }

    read(){
        this.emit(
            'reading'
        );
        console.log(this.words.join(' '));
    }
}

const book=new Book;

book.on(
    'added',
    function(...words){
        console.log('words added : ',words);
        this.read();
    }
);

book.add(
    'once','upon','a','time','in','a','cubicle'
);

Strong Type Checking

event-pubsub uses the strong-type class which provides methods to test all the built in js primatives, objects, classes, and even fancy things like async functions and generators. This should help make sure your code doesn't do unexpected things.

full strong-type documentation

For node

Since we use the same files for node and the browser, we need to emulate a production npm i event-pubsub in the example folder, so be sure to :

first run npm run emulate

then run any of the following examples

node ./example/basic.js
node ./example/miltiple.js
node ./example/extending.js
node ./example/once.js

For the browser

run npm start this will automatically run npm run emulate for you as well.

Then just go to the local server : http://localhost:8000 from here you can see both the examples and the tests. Or go directly to the local example : http://localhost:8000/example/. It actually imports the node example into the browser and runs it, same exact file, no transpiling or custom code for the browser. If you want to transpile though, you can.

How Did I emulate a production install for the module inside itself???

I'm actually pretty pleased with how easy this was. Feel free to use the same type of scripts in your projects. You can even copy paste and just change the repo/module names if you want. Here is the code from my package.json using && is important otherwise your commands will run in parallel, and you really need them to run atomically.

This is needed because we use relative paths in our ES6+ modules to allow the same exact js to work in node and the browser. Its what we have all been waiting for!

 "scripts": {
    "test": "npm run emulate && node ./test/CI.js",
    "start": "npm run emulate && node-http-server port=8000 verbose=true",
    "emulate": "npm i && copyfiles -V \"./!(node_modules)/*\" \"./**!(node_modules)\"  \"./example/node_modules/event-pubsub/\" && copyfiles -V \"./node_modules/**/*\" \"./example/\" && copyfiles -V \"./!(node_modules)/*\" \"./**!(node_modules)\"  \"./test/node_modules/event-pubsub/\" && copyfiles -V \"./node_modules/**/*\" \"./test/\""
},

Testing done with vanilla-test

vanilla-test is a pretty sweet, And minimalist ES6+ testing suite for both the browser and node. You can run the tests with npm test

Also, the tests can be run in the browser if you run npm start and then go to the local server : http://localhost:8000 and click the test link. Also, remember, you should be able to access them via http://[your-ip]:8000 provided your firwall and router are not blocking your ip or ports.

Node vanilla-test screenshot

Chrome vanilla-test screenshot

Chrome Example Screenshot

Edge Example Screenshot

FireFox Nightly Example Screenshot

As of 11/22/2020 FF still does not support private fields or methods in js classes, however, the nightly build has it included behind a flag. With the private field and method flags set to true, FireFox nightly works like a charm.