airwaves

Airwaves

Airwaves is a lightweight pub/sub library that can be used in any JavaScript environment. It has no dependencies.

To communicate over the airwaves, first create a channel:

bbc = new airwaves.Channel

Channels provide methods for broadcasting transmissions and for managing subscriptions to these broadcasts. Each channel operates on a dedicated frequency, so there's no risk of anyone receiving unwanted transmissions.

bbc.subscribe "news", ({name}) -> alert "now playing: #{name}"
bbc.broadcast "news",
  name: "World Business Report"
  desc: "The latest business and finance news from around the world."

This adds a subscriber to "news" broadcasts on the bbc channel. Shortly thereafter, the subscriber learns of the World Business Report broadcast.

---

channel.broadcast(name, args...)

Broadcast args to all those subscribed to name on this channel.

channel.broadcast "delete"
channel.broadcast "rename", "johnsmith", "JohnSmith"
channel.broadcast "resize", width: 1360, height: 859

---

channel.subscribe(name, fn)

Subscribe fn to broadcasts of name on this channel. fn receives the broadcast's values as arguments.

channel.subscribe "hashchange", (hash) -> location.hash = hash

---

channel.unsubscribe(name[, fn])

Unsubscribe fn from broadcasts of name on this channel. If fn is omitted, all subscriptions to broadcasts of name on this channel are cancelled.

# Unsubscribe save handler from "textchange" broadcasts:
channel.unsubscribe "textchange", save

# Unsubscribe all handlers from "resize" broadcasts:
channel.unsubscribe "resize"

---

channel.intercept(name, fn)

Subscribe fn to broadcasts of name on this channel in such a way that it may modify and/or cancel such broadcasts.

Subscribers can receive and respond to broadcasts, but cannot affect them in any way. Interceptors, on the other hand:

• receive broadcasts ahead of subscribers
• can modify broadcasts
• can cancel broadcasts

An interceptor receives the broadcast as its first argument, followed by zero or more arguments representing the broadcast's content:

channel.intercept "print", (broadcast, filename, orientation) ->
  # ...
channel.broadcast "print", "~/Downloads/contract.pdf", "portrait"

An interceptor cancels any broadcast it intercepts unless it invokes the function passed to it as its first argument. The values it passes to this function are received by subscribers (and any remaining interceptors). The no-op interceptor is as follows:

channel.intercept name, (broadcast, args...) ->
  broadcast args...

An interceptor modifies a broadcast by invoking the broadcast function with values different from those it received. This enables an interceptor to, for example, sanitize broadcasts on the fly:

channel.intercept "comment", (broadcast, user, message) ->
  broadcast user, message.replace /wtf/gi, "what on earth"

channel.subscribe "comment", (user, message) ->
  console.log "#{user}: #{message}"

channel.broadcast "comment", "Mr. Badger", "I don't know WTF is going on"
channel.broadcast "comment", "Ken Shabby", "WTF are you talking about?"

# Mr. Badger: I don't know what on earth is going on
# Ken Shabby: what on earth are you talking about?

Interceptors can also be used to suppress invalid broadcasts. For example:

channel.intercept "move", (broadcast, move) ->
  if player is active_player then broadcast move
  else alert "It's not your turn!"

---

Event names

Airwaves supports comma-separated event names, so the following snippets are equivalent:

channel.subscribe 'numerator-change', calculate
channel.subscribe 'denominator-change', calculate

channel.subscribe 'numerator-change, denominator-change', calculate

More accurately, event names are delimited by [,\s]+ (thus cannot contain commas or whitespace).

Testing

make setup
make test