Subcast

A fast, small and dependency free publish subscribe event-bus for the browser and nodejs.

Key features

• fast! really!
• middleware per topic or subtopic
• nested topics using dot notation
• chainable function calls
• no dependencies
• unit tests & 100% coverage

How fast?

Platform info:
==============
   Darwin 17.2.0 x64
   Node.JS: 9.5.0
   V8: 6.2.414.46-node.18
   Intel(R) Core(TM) i7-4850HQ CPU @ 2.30GHz × 8

Suite: Synchronous cases
✔ Direct observer callback                                                           71,882,134 rps
✔ Publish to the root topic with one subscriber                                      41,932,809 rps
✔ Publishing to a nested topic with one subscriber                                   28,820,501 rps
✔ Publishing to a nested topic with subscribers on topic chain                       17,219,133 rps
✔ Publishing to a nested topic with subscribers and middleware on topic chain        17,374,707 rps


Suite: Asynchronous cases 
✔ Direct observer callback                                                            3,527,308 rps
✔ Publish to the root topic with one subscriber                                      14,678,458 rps
✔ Publishing to a nested topic with one subscriber                                   11,500,708 rps
✔ Publishing to a nested topic with subscribers on topic chain                        9,446,315 rps
✔ Publishing to a nested topic with subscribers and middleware on topic chain         7,759,429 rps

How small?

About 2 KB compressed.

Installation

You can install it via NPM.

$ npm install subcast --save

or

$ yarn add subcast

Example Usage

const topics = require('subcast')()
 
topics('foo')
  .subscribe(console.log)
  .publish('Hello World!')
  .publish('Hello again')
  .unsubscribe()
 
topics('foo')
  .use((message, meta, next) => { 
    console.log('foo:', message)
    next(message, meta)
  })
  .subtopic('bar')
  .use((message, meta, next) => {
    console.log('bar:', message)
    next(message, meta)
  })
  .publish('hello') // bar: hello
  .pop()
  .publish('hello') // foo: hello + bar: hello
  .clear()
 
topics('some-topic')
  .once(console.log)
  .publish('hello')   // hello
  .publish('goodbye') // no output
 

Subcast

Constructor for accessing topics, which are created on the fly if necessary. Topics can be nested and each have their own list of subscribers and middleware.

// Creates three nested topics each with it's list of subscribers and middleware.
const fooBarBazTopic = topics('foo.bar.baz')
 
// A subscription to the root topic will get called for all published messages.
const rootTopic = topics()

Arguments

Parameter	Default	Description
name	undefined	if undefined returns the current topic otherwise creates nested topics using . as the seperator.

subscribe

Registers one or more callbacks with the topic and returns the topic. The callback will be called for publications on this topic as well as all subtopics.

// Creates three nested topics each with it's list of subscribers and middleware.
topics('foo.bar.baz')
  .subscribe((message, meta, path) => { /* do something  */ })

Arguments

Parameter	Default	Description
callback		(message, meta) => { /* ... */ } the callback gets the published message as well as a meta object that contains a unique contextId, the originalPath on which the message was published. Other properties may also have been added by middleware functions.

once

Similar to subscribe but will automatically unsubscribe after having received the next message.

// Creates three nested topics each with it's list of subscribers and middleware.
topics('foo.bar.baz')
  .subscribeOnce((message, meta, path) => { /* do something  */ })

Arguments

Parameter	Default	Description
callback		See subscribe

publishSync

Publishes a message synchronously to a topic and all it's parent topics.

The function returns the topic and upon return all subscribers will have received the message.

// Creates three nested topics each with it's list of subscribers and middleware.
topics('foo.bar.baz')
  .publishSync({cmd:'do-this', with:'that'})

Arguments

Parameter	Default	Description
message	Any	The message get posted as-is unless modified by middleware functions

publishAsync

Publishes a message asynchronously to a topic and all it's parent topics.

The function returns the topic subscribers will have not have received the message. The messages will be received during the next event loop.

// Creates three nested topics each with it's list of subscribers and middleware.
topics('foo.bar.baz')
  .publishAsync({cmd:'do-this', with:'that'})

Arguments

Parameter	Default	Description
message	Any	The message get posted as-is unless modified by middleware functions

unsubscribe

Unregisters one or more callbacks from the topic. If no arguments are provided then all subscribers are unregistered.

// Creates three nested topics each with it's list of subscribers and middleware.
topics('foo.bar.baz')
  .unsubscribe(fooBarBazMessageHandler1, fooBarBazMessageHandler2)

Arguments

Parameter	Default	Description
callbacks		If undefined will unsubscribe all subscribers from the topic otherwise only those that were specified.

clear

Unregisters all callers from a topic and its subtopics. Calling this on the root topic will clear all subscripitions.

// Creates three nested topics each with it's list of subscribers and middleware.
topics('foo.bar.baz')
  .clear()

Arguments

Parameter	Default	Description
	If undefined will unsubscribe all subscribers otherwise only those listed in the callback list.

subtopic

From an existing topic, returns a subtopic with the given name

// Creates three nested topics each with it's list of subscribers and middleware.
// This is equivalent to topics('foo.bar.baz')
topics('foo')
  .subtopic('bar')
    .subtopic('baz')

Arguments

Parameter	Default	Description
name		If undefined will return the current topic otherwise will create nested topics as necessary and return the requested one.

pop

Returns the parent topic or the root topic if no parent exists.

topics('foo')
  .subtopic('bar')
  .pop()  

use

Registers a middleware function with a topic. It will be applied to messages for this topic and all subtopics. Middleware functions get called in the order that they are added and from parent to child.

// Creates three nested topics each with it's list of subscribers and middleware.
topics('foo')
  .use((message, meta, next) =>{ 
     // Do something...
     next(message, meta)
     // Do something else...
  })

Arguments

Parameter	Default	Description
callbacks		One or more functions with the (message, meta, next) => { ... } signature. Please note that if next is not called then the message won't be published.

use

Unregisters a middleware function from the topic.

// Creates three nested topics each with it's list of subscribers and middleware.
topics('foo')
  .unuse(myMiddleware)

Arguments

Parameter	Default	Description
callbacks		One or more functions to remove from the middleware chain.

Contribution

Please send pull requests improving the usage and fixing bugs, improving documentation and providing better examples, or providing some testing, because these things are important.

License

topics is available under the MIT license.