pubsub-js

PubSubJS

PubSubJS is a topic-based publish/subscribe library written in JavaScript.

PubSubJS has synchronisation decoupling, so topics are published asynchronously. This helps keep your program predictable as the originator of topics will not be blocked while consumers process them.

For the adventurous, PubSubJS also supports synchronous topic publication. This can give a speedup in some environments (browsers, not all), but can also lead to some very difficult to reason about programs, where one topic triggers publication of another topic in the same execution chain.

Single process

PubSubJS is designed to be used within a single process, and is not a good candidate for multi-process applications (like Node.js – Cluster with many sub-processes). If your Node.js app is a single process app, you're good. If it is (or is going to be) a multi-process app, you're probably better off using redis Pub/Sub or similar

Key features

Dependency free
Synchronization decoupling
ES3 compatible. PubSubJS should be able to run everywhere that can execute JavaScript. Browsers, servers, ebook readers, old phones, game consoles.
AMD / CommonJS module support
No modification of subscribers (jQuery custom events modify subscribers)
Easy to understand and use (thanks to synchronization decoupling)
Small(ish), less than 1kb minified and gzipped

Getting PubSubJS

There are several ways of getting PubSubJS

Download a tagged version from GitHub
Install via npm (npm install pubsub-js)
Install via bower (bower install pubsub-js)
Use it via CDN directly (http://www.jsdelivr.com/#!pubsubjs)

Examples

Basic example

// create a function to subscribe to topics 
var mySubscriber = function( msg, data ){
    console.log( msg, data );
};
 
// add the function to the list of subscribers for a particular topic 
// we're keeping the returned token, in order to be able to unsubscribe 
// from the topic later on 
var token = PubSub.subscribe( 'MY TOPIC', mySubscriber );
 
// publish a topic asyncronously 
PubSub.publish( 'MY TOPIC', 'hello world!' );
 
// publish a topic syncronously, which is faster in some environments, 
// but will get confusing when one topic triggers new topics in the 
// same execution chain 
// USE WITH CAUTION, HERE BE DRAGONS!!! 
PubSub.publishSync( 'MY TOPIC', 'hello world!' );

Cancel specific subscription

// create a function to receive the topic 
var mySubscriber = function( msg, data ){
    console.log( msg, data );
};
 
// add the function to the list of subscribers to a particular topic 
// we're keeping the returned token, in order to be able to unsubscribe 
// from the topic later on 
var token = PubSub.subscribe( 'MY TOPIC', mySubscriber );
 
// unsubscribe this subscriber from this topic 
PubSub.unsubscribe( token );

Cancel all subscriptions for a function

// create a function to receive the topic 
var mySubscriber = function( msg, data ){
    console.log( msg, data );
};
 
// unsubscribe mySubscriber from ALL topics 
PubSub.unsubscribe( mySubscriber );

Clear all subscriptions for a topic

PubSub.subscribe('a', myFunc1);
PubSub.subscribe('a.b', myFunc2);
PubSub.subscribe('a.b.c', myFunc3);
 
PubSub.unsubscribe('a.b');
// no further notications for 'a.b' and 'a.b.c' topics 
// notifications for 'a' will still get published

Clear all subscriptions

PubSub.clearAllSubscriptions();
// all subscriptions are removed

Hierarchical addressing

// create a subscriber to receive all topics from a hierarchy of topics 
var myToplevelSubscriber = function( msg, data ){
    console.log( 'top level: ', msg, data );
}
 
// subscribe to all topics in the 'car' hierarchy 
PubSub.subscribe( 'car', myToplevelSubscriber );
 
// create a subscriber to receive only leaf topic from hierarchy op topics 
var mySpecificSubscriber = function( msg, data ){
    console.log('specific: ', msg, data );
}
 
// subscribe only to 'car.drive' topics 
PubSub.subscribe( 'car.drive', mySpecificSubscriber );
 
// Publish some topics 
PubSub.publish( 'car.purchase', { name : 'my new car' } );
PubSub.publish( 'car.drive', { speed : '14' } );
PubSub.publish( 'car.sell', { newOwner : 'someone else' } );
 
// In this scenario, myToplevelSubscriber will be called for all 
// topics, three times in total 
// But, mySpecificSubscriber will only be called once, as it only 
// subscribes to the 'car.drive' topic

Tips

Use "constants" for topics and not string literals. PubSubJS uses strings as topics, and will happily try to deliver your topics with ANY topic. So, save yourself from frustrating debugging by letting the JavaScript engine complain when you make typos.

Example of use of "constants"

// BAD 
PubSub.subscribe("hello", function( msg, data ){
    console.log( data )
});
 
PubSub.publish("helo", "world");
 
// BETTER 
var MY_TOPIC = "hello";
PubSub.subscribe(MY_TOPIC, function( msg, data ){
    console.log( data )
});
 
PubSub.publish(MY_TOPIC, "world");

Immediate Exceptions for stack traces in developer tools

As of versions 1.3.2, you can force immediate exceptions (instead of delayed execeptions), which has the benefit of maintaining the stack trace when viewed in dev tools.

This should be considered a development only option, as PubSubJS was designed to try to deliver your topics to all subscribers, even when some fail.

Setting immediate exceptions in development is easy, just tell PubSubJS about it after it's been loaded.

PubSub.immediateExceptions = true;

Plugin for jQuery

By default PubSubJS can be used in any browser or CommonJS environment, including node. Additionally, PubSubJS can be built specifically for jQuery using Rake.

$ rake jquery

or using Grunt

$ grunt jquery

Produces jquery.pubsub.js

Use with jQuery

var topic = 'greeting',
    data = 'world',
    subscriber = function sayHello( data ){
        console.log( 'hello ' + data );
    };
 
// add a subscription 
var token = $.pubsub('subscribe', topic, subscriber );
 
// unsubscribing 
$.pubsub('unsubscribe', token);         // remove a specific subscription 
$.pubsub('unsubscribe', subscriber);    // remove all subscriptions for subscriber 
 
// publishing a topic 
$.pubsub('publish', topic, data);
 
// publishing topic syncronously 
$.pubsub('publishSync', topic, data);

In the jQuery build, the global PubSub global is still available, so you can mix and match both Pubsub and $.pubsub as needed.

There is also an article about Using PubSubJS with jQuery

Contributing to PubSubJS

Please see CONTRIBUTING.md

Future of PubSubJS

Better and more extensive usage examples

More about Publish/Subscribe

Versioning

PubSubJS uses Semantic Versioning for predictable versioning.

Changelog

Please see https://github.com/mroderick/PubSubJS/releases

License

MIT: http://mrgnrdrck.mit-license.org

Alternatives

These are a few alternative projects that also implement topic based publish subscribe in JavaScript.

http://www.joezimjs.com/projects/publish-subscribe-jquery-plugin/
http://amplifyjs.com/api/pubsub/
http://radio.uxder.com/ — oriented towards 'channels', free of dependencies
https://github.com/pmelander/Subtopic - supports vanilla, underscore, jQuery and is even available in NuGet