PubSub

An implementation of Publish Subscribe pattern in JavaScript, in both browser and server compatible versions

Setup

Browser

<script src="pubsub.js"></script>

Server (requires node version 4 or higher)

Install from npm register

npm install jspubsub

Import or require in your module

import PubSub from 'jspubsub';

const PubSub = require('jspubsub');

Usage

Set a new subscriber object calling the Subscribe class with a topic and a callback assigned as parameters

let subscriber = new PubSub.Subscribe('test', (data) => {
	console.log(data.test)
});

The executor callback will be fired when the static 'publish' method is called with the related toipc as first argument. You can pass moreover arbitrary object data as the second parameter

PubSub.publish('test', { test: 'very nice test' });
// console logs 'very nice test'

Singleton

You can subscribe events to be fired once

let subscriber = new PubSub.SubscribeOnce('test', () => {
	console.log('this will be printed once')
});

for (let i = 0; i < 5; i++) {
	PubSub.publish('test');
}
// console logs 'this will be printed once' just once

Note about async and sync publishing

PubSub's publish method has been designed to be asynchronous, so topic published will not block the main thread and your program will be more predictable. If you want instead to do actions that need to be executend soon there is a 'publishSync' method:

let result = null;

let subscriber = new PubSub.Subscribe('test', (data) => {
	result = data.test;
});

PubSub.publish('test', { test: 'very nice test' });
console.log(result) // null, beacuse execution of the topic is async so the callback has been pushed at the end of the queue

PubSub.publishSync('test', { test: 'very nice test' });
console.log(result) // 'very nice test'

Working with the subscriber instance

Count getter

Every instance of PubSub.Subscribe class has a getter that expose the number of times the topic has been called, you might find this useful for debugging:

let subscriber = new PubSub.Subscribe('test', (data) => {
	console.log(data.test)
});
PubSub.publishSync('test', { test: 'very nice test' });
for (let i = 0; i < 5; i++) {
	PubSub.publish('test');
}
console.log(subscriber.count) // 5

Note that we have used 'publishSync' beacuse we wanted to check the actual count within the current thread, so changed caused by the topic's publishing had to be triggered and executed immediately.

Remove the subscription

With the 'remove' method, when called we disconnect the subscriber from listening the topic it was subscribed to:

let subscriber = new PubSub.Subscribe('test', (data) => {
	console.log(data.test)
});
subscriber.remove();
PubSub.publish('test', { test: 'very nice test' });
// console logs nothing

Tests

You can find tests in test/test.js Install dependencies first with npm install and run tests with npm test command.