dendrite

An extended Observer pattern implementation, worked at any JavaScript environment

npm install dendrite
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dendrite

An extended Observer pattern implementation, (must)worked at any JavaScript environment.

It designed to simplify creation of low coupling and high cohesion systems with upgraded Dendrite realization.

Dendrite was created on base of JZ-Publish-Subscribe-jQuery-Plugin, plus have some unique methods like #publishAsync() and #subscribeGuarded().

Dendrite build as CommonJS module, but actually it may be used in browser too. You need to resolve underscore or lodash dependency and get packed verson (see browser/dendrite.js or browser/dendrite.js.min ) or pack all you project with clinch.

Description:

Dendrite, as JZ-Publish-Subscribe-jQuery-Plugin successor implement all forerunner methods and may be used as replacement with slightly changes in code.

Dendrite created to be used as local object, not one huge global observer. Its possible to have any numbers of dendrite objects without any interactions.

To have some more benefits from Dendrite you should be used #publishAsync() and #subscribeGuarded() methods. These methods may reduce GUI latency and simplify exception handling with callbacks.

Moreover - Dendrite may attach listeners to 'subscribe' and 'unsubscribe' events, its allow add activity to listened topics and stop it on unlistened, for example.

See the examples below or test files.

Documentation:

See full documentation, created with codo.

Also quick link to module interface docs - Class: Dendrite.

Install:

npm install dendrite

Usage:

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

At first you must create Dendrite object to interact with it

Dendrite = require 'dendrite'
dendrite_obj = new Dendrite

Constructor have some options on create

verbose : ['debug'|'warning'|'error'|'silent'] # verbose levels placed by decrementing

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

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

handle = dendrite_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 = dendrite_obj.subscribe("foo", obj.func, obj)

Subscribing with watchdog:

Guarded subscription give as powerful technique to manage errors in subscribed functions

dendrite_obj = new Dendrite verbose : 'silent'

callback = (topic, data) -> throw Error "Die at #{topic}"
watchdog = (err, options) -> 
  console.log "Error string: | #{err} |"
  console.log "Error detail", options
  null
handle = dendrite_obj.subscribeGuarded 'foo', callback, watchdog

dendrite_obj.publish 'foo', 'some data'

return to console

Error string: | Error: Die at foo |
Error detail { topic: 'foo',
  callback: [Function],
  object: {},
  data: [ 'some data' ] }

Now subscribed object MAY decide how support itself errors

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

dendrite_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

dendrite_obj.unsubscribe("foo bar", callback_reference, obj)
# or
dendrite_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

dendrite_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

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

Or you may send task to queue for asynchronous execution (see ./tests for more examples)

dendrite_obj.publishAsync("foo bar", "This is some data") 

Get list of listened topics

This method will return list of topics with listiners on it.

dendrite_obj.getListenedTopicsList()

Test is topic have listeners

This method will return boolean value - is topic have listeners or not

is_listened = dendrite_obj.isTopicListened 'foo'

Attach callback to dendrite object on subscribe/unsubscribe events

This method attach listeners to internal events - subscribe/unsubscribe. May be helpful if logic request ACTIVE observer

handler = dendrite_obj.on 'subscribe', (topic) -> console.log "subscribed to |#{topic}|"

Detach callback from dendrite object on subscribe/unsubscribe events

This method dettach listeners from internal events - subscribe/unsubscribe.

dendrite_obj.off 'subscribe'  # remove ALL listeners
dendrite_obj.off handler      # remove ONLY one listener

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.

Need you help!

If you feel ability to translate good Russain README (I'm add it soon) to correct English - please, ping me. Thanks in advance!

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