https://github.com/georapbox/pubsub

Javascript implementation of the Publish/Subscribe pattern.
https://github.com/georapbox/pubsub
callback event-emitter events javascript publish publish-subscribe pubsub pubsub-instance subscribe subscription topic
Last synced: 5 months ago
JSON representation
Javascript implementation of the Publish/Subscribe pattern.
Host: GitHub
URL: https://github.com/georapbox/pubsub
Owner: georapbox
License: mit
Created: 2014-09-26T15:46:02.000Z (about 11 years ago)
Default Branch: master
Last Pushed: 2023-01-06T18:29:12.000Z (almost 3 years ago)
Last Synced: 2024-11-01T11:51:35.656Z (about 1 year ago)
Topics: callback, event-emitter, events, javascript, publish, publish-subscribe, pubsub, pubsub-instance, subscribe, subscription, topic
Language: JavaScript
Homepage:
Size: 479 KB
Stars: 29
Watchers: 3
Forks: 7
Open Issues: 2
Metadata Files:
- Readme: README.md
- Changelog: CHANGELOG.md
- License: LICENSE
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# PubSub

Javascript implementation of the [Publish/Subscribe](http://en.wikipedia.org/wiki/Publish%E2%80%93subscribe_pattern) pattern.

## Install

### npm

```sh

$ npm install PubSub

```

## Usage

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

### Using ESM import statement

```js

import PubSub from 'PubSub';

```

### Using CommonJS require statement

```js

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; 

```

### Old school browser global

```html

```

## API

* [PubSub](#PubSub)

    * [new PubSub([options])](#new_PubSub_new)

    * _instance_

        * [.subscribe(topic, callback, [once])](#PubSub+subscribe) ⇒ number

        * [.subscribeOnce(topic, callback)](#PubSub+subscribeOnce) ⇒ number

        * [.publish(topic, [...data])](#PubSub+publish) ⇒ boolean

        * [.publishSync(topic, [...data])](#PubSub+publishSync) ⇒ boolean

        * [.unsubscribe(topic)](#PubSub+unsubscribe) ⇒ boolean \| string

        * [.unsubscribeAll()](#PubSub+unsubscribeAll) ⇒ [PubSub](#PubSub)

        * [.hasSubscribers([topic])](#PubSub+hasSubscribers) ⇒ boolean

        * [.subscribers()](#PubSub+subscribers) ⇒ object

        * [.subscribersByTopic(topic)](#PubSub+subscribersByTopic) ⇒ array

        * [.alias(aliasMap)](#PubSub+alias) ⇒ [PubSub](#PubSub)

    * _static_

        * [.createInstance([options])](#PubSub.createInstance) ⇒ [PubSub](#PubSub)



### new PubSub([options])

Creates a PubSub instance.

#### Available options

| Param | Type | Default | Description |

| --- | --- | --- | --- |

| immediateExceptions¹ | boolean | false | Force immediate exceptions (instead of delayed exceptions). |

¹ *Before version 3.6.0 PubSub would fail to deliver your topics to all subscribers if one or more failed (see issue [#4](https://github.com/georapbox/PubSub/issues/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.*

## Public Methods



### subscribe(topic, callback, [once]) ⇒ number

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](#PubSub)  

**Returns**: number - The topic's token  

| Param | Type | Default | Description |

| --- | --- | --- | --- |

| topic | string |  | The topic's name |

| callback | function |  | Callback function to execute on event, taking two arguments:        - {*} data The data passed when publishing an event        - {object} The topic's info (name & token) |

| [once] | boolean | false | Checks if event will be triggered only one time |

**Example**  

```js

const pubsub = new PubSub();

const onUserAdd = pubsub.subscribe('user_add', (data, topic) => {

  console.log('User added');

  console.log('user data:', data);

});

```



### subscribeOnce(topic, callback) ⇒ number

Subscribe to events of interest setting a flag

indicating the event will be published only one time.

**Kind**: instance method of [PubSub](#PubSub)  

**Returns**: number - The topic's token  

| Param | Type | Description |

| --- | --- | --- |

| topic | string | The topic's name |

| callback | function | Callback function to execute on event, taking two arguments:        - {*} data The data passed when publishing an event        - {object} The topic's info (name & token) |

**Example**  

```js

const pubsub = new PubSub();

const onUserAdd = pubsub.subscribeOnce('user_add', (data, topic) => {

  console.log('User added');

  console.log('user data:', data);

});

```



### publish(topic, [data]) ⇒ boolean

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](#PubSub)  

**Returns**: boolean - Returns `true` if topic exists and event is published; otheriwse `false`  

| Param | Type | Description |

| --- | --- | --- |

| topic | string | The topic's name |

| [data] | ...\* | The data to be passed to its subscribers |

**Example**  

```js

const pubsub = new PubSub();

pubsub.publish('user_add', {

  firstName: 'John',

  lastName: 'Doe',

  email: 'johndoe@gmail.com'

});

```



### publishSync(topic, [data]) ⇒ boolean

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

**Kind**: instance method of [PubSub](#PubSub)  

**Returns**: boolean - Returns `true` if topic exists and event is published; otheriwse `false`  

| Param | Type | Description |

| --- | --- | --- |

| topic | string | The topic's name |

| [data] | ...\* | The data to be passed to its subscribers |

**Example**  

```js

const pubsub = new PubSub();

pubsub.publishSync('user_add', {

  firstName: 'John',

  lastName: 'Doe',

  email: 'johndoe@gmail.com'

});

```



### unsubscribe(topic) ⇒ boolean \| string

Unsubscribes from a specific topic, based on the topic name,

or based on a tokenized reference to the subscription.

**Kind**: instance method of [PubSub](#PubSub)  

**Returns**: boolean \| string - Returns `false` if `topic` does not match a subscribed event; otherwise the topic's name  

| Param | Type | Description |

| --- | --- | --- |

| topic | string \| number | Topic's name or subscription reference |

**Example**  

```js

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);

```



### unsubscribeAll() ⇒ [PubSub](#PubSub)

Clears all subscriptions whatsoever.

**Kind**: instance method of [PubSub](#PubSub)  

**Returns**: [PubSub](#PubSub) - The PubSub instance.  

**Example**  

```js

const pubsub = new PubSub();

pubsub.subscribe('message1', () => {});

pubsub.subscribe('message2', () => {});

pubsub.subscribe('message3', () => {});

pubsub.unsubscribeAll();

pubsub.hasSubscribers(); // -> false

```



### hasSubscribers([topic]) ⇒ boolean

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](#PubSub)  

**Returns**: boolean - Returns `true` there are subscribers; otherwise `false`  

| Param | Type | Description |

| --- | --- | --- |

| [topic] | string | The topic's name to check |

**Example**  

```js

const pubsub = new PubSub();

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

pubsub.hasSubscribers('message');

// -> true

```



### subscribers() ⇒ object

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](#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**  

```js

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] }

```



### subscribersByTopic(topic) ⇒ array

Gets subscribers for a specific topic.

**Kind**: instance method of [PubSub](#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.

| Param | Type | Description |

| --- | --- | --- |

| topic | String | The topic's name to check for subscribers |

**Example**  

```js

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 []

```



### alias(aliasMap) ⇒ [PubSub](#PubSub)

Creates aliases for public methods.

**Kind**: instance method of [PubSub](#PubSub)  

**Returns**: [PubSub](#PubSub) - The PubSub instance.  

| Param | Type | Description |

| --- | --- | --- |

| aliasMap | Object | A plain object that maps the public methods to their aliases. |

**Example**  

```js

const pubsub = new PubSub().alias({

  subscribe: 'on',

  subscribeOnce: 'once',

  publish: 'trigger',

  publishSync: 'triggerSync',

  unsubscribe: 'off',

  hasSubscribers: 'has'

});

```

## Static methods



### PubSub.createInstance([options]) ⇒ [PubSub](#PubSub)

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](#PubSub)  

**Returns**: [PubSub](#PubSub) - The PubSub constructor.  

**Example**  

```js

const pubsub = PubSub.createInstance();

```

## Changelog

For API updates and breaking changes, check the [CHANGELOG](https://github.com/georapbox/PubSub/blob/master/CHANGELOG.md).

## More about Publish/Subscribe pattern

- [The Observer Pattern - Addy Osmani](https://addyosmani.com/resources/essentialjsdesignpatterns/book/#observerpatternjavascript)

- [Publish–Subscribe pattern - Wikipedia](http://en.wikipedia.org/wiki/Publish%E2%80%93subscribe_pattern)

## License

[The MIT License (MIT)](https://github.com/georapbox/PubSub/blob/master/LICENSE)
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