hamradio

hamradio was designed based off the great ideas in many other pubsub modules. I would not have made it but I had one little requirement that I couldn't find elsewhere: I needed to publish events to other browser tabs. In hamradio, this is accomplished through BroadcastChannel which along with Promises and => are the only "dependencies" of the module.

hamradio provides the following flavors of pubsub:

• asynchronous - hamradio does not execute subscribed functions synchronously. This has the advantage of not breaking code that publishes unexpectedly, but the disadvantage of losing track of call stacks to where the publishing event happened
• subchannels - hamradio allows for breaking communications into subchannels and relaying any published events up the chain to parent channels. That means that listening on parent channels allows you to receive any events published on its subchannels.
• multi-tab - the signature feature of hamradio is that it can communicate across browser contexts. Assuming both sets of code in each context use hamradio, events are sent and received between the hamradio instances seamlessly.

hamradio is intended to be used as an npm module.

Installing

npm install hamradio

Usage

A simple example follows:

import hamradio from 'hamradio'

const subscription = hamradio.subscribe(
  'ham/radio',
  (name, data) => console.log(name, data)
)

hamradio.publish('ham/radio', 'foo')
// expect to see "ham/radio foo" in the console

hamradio.publish('ham/radio/test', {bar: baz})
// expect to see "ham/radio/test {bar: baz}" in the console

hamradio.publish('ham', 'is a sweet meat')
// expect to see nothing in the console because no one's listening to the parent

subscription.unsubscribe()

hamradio.publish('ham/radio', 'again')
// expect to see nothing in the console because we unsubscribed

console.log('A word on timing')

A word on timing, hamradio runs the subscribed handlers asynchronously. In the example above, none of the console.log events would happen until after "A word on timing" had been logged. Ordering of which subscribed handlers execute first is arbitrary.

To help with synchronicity, the publish function returns a promise that will be accepted after all handler functions have completed. This promise only cares about the local context. It has no reference to when other hamradio or other handlers execute in other contexts. The promise will pass through any exceptions raised by the handler functions.

Channels and Handlers

Channels are interfaced with primarily by using a string name. When publishing and subscribing, the string name should be fully qualified with all parent channels represented. For example "ham/radio" represents the "radio" subchannel inside the "ham" channel. There is a small overhead for using deeply nested channels as parent channels are created as necessary on subscription or publishing.

When subscribing to a channel, a handler function must be provided. Handler functions receive two parameters when called, the name of the channel, and data published to the channel. The channel name is included to distinguish whether the data was published on the subscribed channel or one of its subchannels.

Publishing to a channel will trigger calls to the handlers of a particular channel as well as all of its parents.

Other Contexts

Because hamradio uses BroadcastChannel, other contexts do not need to use hamradio to intercept events published by hamradio. They can simply create a BroadcastChannel instance using the name of the channel and communicate with hamradio using the postMessage and onmessage protocols as usual.

hamradio is most useful when a pubsub model is needed AND there is a requirement to communicate with other browser contexts.