whet.observer

A standalone Observer that actually works on node.js, adapted from Publish/Subscribe plugin for jQuery

Description:

This script implement Observer pattern in Object Oriented-manner.

I find this mush more predictable than one huge global observer.

Also its allow you to operate to multiple topics just by separating the topic names with a space, as JZ-Publish-Subscribe-jQuery-Plugin do it.

See the examples below or test files.

Usage:

All examples use CoffeeScript, you may use plain JS instead (but why?).

At first you must create Observer object to interact with it

Observer = require 'whet.observer'
observer_obj = new Observer

Subscribing:

Subscribe to a single topic called 'foo'

The callback function receives two arguments:

• data: any data that the publisher sent
• topic: the topic that was published to that called the function

Note: #subscribe() returns a 'handle' that can be used to unsubscribe easily

handle = observer_obj.subscribe("foo", (topic, data) -> console.log data, topic )

Subscribe to multiple topics at once 'foo', 'bar', and 'baz' are three different topics

handle = observer_obj.subscribe("foo bar baz", (topic, data) -> console.log data, topic )

Subscribe with a context Callback now has its this variable assigned to the specified object

obj = 
  internal_data: 0
  func: (topic, data) -> console.log data, topic, @internal_data

handle = observer_obj.subscribe("foo", obj.func, obj)

Unsubscribing:

Unsubscribe using the handle gained from calling #subscribe(). The callback that was sent into the #subscribe() call that you retrieved the handle from will be unsubscribed from all of the topics subscribed to

observer_obj.unsubscribe(handle)

Unsubscribe by specifying the topics, callback, and context (if one was when subscribed). Note: if you use an anonymous in the #subscribe() call, you can retrieve a reference to the callback from the handle's 'callback' property

observer_obj.unsubscribe("foo bar", callback_reference, obj)
# or
observer_obj.unsubscribe("foo bar", handle.callback);

Using the second syntax is useful if you used an anonymous function and got the handle, but don't want to unsubscribe from all of the topics.

Unsubscribe all callbacks from 1+ topics If you skip giving a callback as a parameter, it'll unsubscribe all functions from the topic(s) given

observer_obj.unsubscribe("foo bar")

Publishing:

Publish to a topic (or topics) When you publish, you may send data to the subscribers, or you can leave the parameter empty if you have no particular data to send. The data does not have a particular format that it must be in, giving you the flexibility to use it in whatever way is appropriate for your application

observer_obj.publish("foo bar", "This is some data")

General Notes

Topics:

Topics can use any name that can also be used as a property name. Since the topic is always retrieved using the bracket notation (e.g. object["prop"]), as opposed to the dot notation (e.g. object.prop), you are allowed to use a large numbers of characters that aren't legal for variable names, such as slashes ("/") or periods ("."). You cannot, however, use a space (" ") because this is the character that separates multiple topics. All three functions (subscribe, unsubscribe, and publish) are able to take one or multiple topics (separated by a space).

Callback Context:

When a callback function is invoked, it is called in the context of blank object. This means that this === {} inside of your function. You may use you own object instead, passed it as context object.

Handle:

The handle that is returned from the #subscribe() function is simply an object with three properties, named "topics", "callback", and "context" that correspond to the three parameters that you sent in (or context will be a blank object if no context was provided):

handle =
  topics : "the topics you sent in"
  callback : (topic, data)-> 
    // this is the callback function you sent in
  context : contextObjYouSentIn || {}

Callback Topic Argument:

The first argument that the callback receives is the topic in which the function was subscribed and invoked from. This will always be a string containing only one topic, even if the #publish() function is called with multiple topics because the callback will be run once for each individual topic that is published.