Javascript implementation of the Publish/Subscribe pattern.

$ npm install PubSub

The library is exported in UMD, CommonJS, and ESM formats. You can import it the following ways:

import PubSub from 'PubSub';

const PubSub = require('PubSub');

// If you use a bundler like Webpack, you may need to import it the following way 
// as it might try to use the ESM module instead of the CommonJS.
const PubSub = require('PubSub').default; 

<script src="https://unpkg.com/PubSub"></script>

• PubSub
  • new PubSub([options])
  • instance
    • .subscribe(topic, callback, [once]) ⇒ number
    • .subscribeOnce(topic, callback) ⇒ number
    • .publish(topic, [...data]) ⇒ boolean
    • .publishSync(topic, [...data]) ⇒ boolean
    • .unsubscribe(topic) ⇒ boolean | string
    • .unsubscribeAll() ⇒ PubSub
    • .hasSubscribers([topic]) ⇒ boolean
    • .subscribers() ⇒ object
    • .subscribersByTopic(topic) ⇒ array
    • .alias(aliasMap) ⇒ PubSub
  • static
    • .createInstance([options]) ⇒ PubSub

Creates a PubSub instance.

¹ Before version 3.6.0 PubSub would fail to deliver your topics to all subscribers if one or more failed (see issue #4). As of version 3.6.0 PubSub handles this by delaying thrown exceptions by default. You can set immediateExceptions to true or any truthy value in order to maintain the stack trace for development reasons but this is not recommended for production.

Subscribe to events of interest with a specific topic name and a callback function, to be executed when the topic/event is observed.

Kind: instance method of PubSub
Returns: number - The topic's token

Example

const pubsub = new PubSub();

const onUserAdd = pubsub.subscribe('user_add', (data, topic) => {
  console.log('User added');
  console.log('user data:', data);
});

Subscribe to events of interest setting a flag indicating the event will be published only one time.

Kind: instance method of PubSub
Returns: number - The topic's token

Example

const pubsub = new PubSub();

const onUserAdd = pubsub.subscribeOnce('user_add', (data, topic) => {
  console.log('User added');
  console.log('user data:', data);
});

Publishes a topic asynchronously, passing the data to its subscribers.
Asynchronous publication helps in that the originator of the topics will not be blocked while consumers process them.
For synchronous topic publication check publishSync.

Kind: instance method of PubSub
Returns: boolean - Returns true if topic exists and event is published; otheriwse false

Example

const pubsub = new PubSub();

pubsub.publish('user_add', {
  firstName: 'John',
  lastName: 'Doe',
  email: '[email protected]'
});

Publishes a topic synchronously, passing the data to its subscribers.

Kind: instance method of PubSub
Returns: boolean - Returns true if topic exists and event is published; otheriwse false

Example

const pubsub = new PubSub();

pubsub.publishSync('user_add', {
  firstName: 'John',
  lastName: 'Doe',
  email: '[email protected]'
});

Unsubscribes from a specific topic, based on the topic name, or based on a tokenized reference to the subscription.

Kind: instance method of PubSub
Returns: boolean | string - Returns false if topic does not match a subscribed event; otherwise the topic's name

Example

const pubsub = new PubSub();

// Unsubscribe using the topic's name.
pubsub.unsubscribe('user_add');

// Unsubscribe using a tokenized reference to the subscription.
pubsub.unsubscribe(onUserAdd);

Clears all subscriptions whatsoever.

Kind: instance method of PubSub
Returns: PubSub - The PubSub instance.
Example

const pubsub = new PubSub();

pubsub.subscribe('message1', () => {});
pubsub.subscribe('message2', () => {});
pubsub.subscribe('message3', () => {});
pubsub.unsubscribeAll();
pubsub.hasSubscribers(); // -> false

Checks if there are subscribers for a specific topic. If topic is not provided, checks if there is at least one subscriber.

Kind: instance method of PubSub
Returns: boolean - Returns true there are subscribers; otherwise false

Example

const pubsub = new PubSub();

pubsub.on('message', data => console.log(data));

pubsub.hasSubscribers('message');
// -> true

Gets all the subscribers as a set of key value pairs that represent the topic's name and the event listener(s) bound.

Kind: instance method of PubSub
Returns: object - A readonly object with all subscribers.
Note: Mutating the result of this method does not affect the real subscribers. This is for reference only.
Example

const pubsub = new PubSub();

pubsub.subscribe('message', listener);
pubsub.subscribe('message', listener);
pubsub.subscribe('another_message', listener);

pubsub.subscribers();
// -> Object { message: Array[2], another_message: Array[1] }

Gets subscribers for a specific topic.

Kind: instance method of PubSub
Returns: array - A copy array of all subscribers for a topic if exist; otherwise an empty array
Note: Mutating the result of this method does not affect the real subscribers. This is for reference only.

Example

const pubsub = new PubSub();

pubsub.subscribe('message', listener1);
pubsub.subscribeOnce('message', listener2);
pubsub.subscribe('another_message', listener1);

pubsub.subscribersByTopic('message');
// -> Array [{token: 0, once: false, callback: listener1()}, {token: 1, once: true, callback: listener2()}]

pubsub.subscribersByTopic('another_message');
// -> Array [{token: 2, once: false, callback: listener1()}]

pubsub.subscribersByTopic('some_message_not_existing');
// -> Array []

Creates aliases for public methods.

Kind: instance method of PubSub
Returns: PubSub - The PubSub instance.

Example

const pubsub = new PubSub().alias({
  subscribe: 'on',
  subscribeOnce: 'once',
  publish: 'trigger',
  publishSync: 'triggerSync',
  unsubscribe: 'off',
  hasSubscribers: 'has'
});

Creates a PubSub instance. This is an alternative way to create a new instance if you don't prefer using the new keyword.

Kind: static method of PubSub
Returns: PubSub - The PubSub constructor.
Example

const pubsub = PubSub.createInstance();

For API updates and breaking changes, check the CHANGELOG.

• The Observer Pattern - Addy Osmani
• Publish–Subscribe pattern - Wikipedia

The MIT License (MIT)