Mediator.js

Version 0.9.0

Breaking changes since version 0.7.0: see changelog below

For more information, please see

Relevant blog post

View the project on Github

View the documentation

Documentation built using Paige

A light utility class to help implement the Mediator pattern for easy eventing

Mediator is a simple class that allows you to register, unregister, and call subscriber methods to help event-based, asyncronous programming. Its purpose is to make the usage of WebSockets, Ajax calls, DOM events, or any other asynchronous operations easy to maintain and test.

1.12kb, minifed and gzipped

Why?

My specific use case: bind elements easily for WebSocket callbacks. But, you may find usage in it for all kinds of things: as an event management system, to decouple calls between javascript functions, Ajax request callbacks, and more. There's an excellent online book that talks about Mediators more in detail by Addy Osmani.

Usage

You can register events with the mediator two ways using channels. You can add a predicate to perform more complex matching. Instantiate a new mediator, and then you can being subscribing, removing, and publishing.

Subscription signature:

Mediator.subscribe(channel, callback, <options>, <context>);
Mediator.publish(channel, <data, data, ... >)
Mediator.remove(channel, <identifier>)

Additionally, on and bind are aliased to subscribe, and trigger and emit are bound to publish. off is an alias for remove. You can use once to subscribe to an event that should only be fired once.

Subscriber signature:

function(<data, data ...>, channel);

The channel is always returned as the last argument to subscriber functions.

Mediator.subscribe options (all are optional; default is empty):

{
  predicate: function(*args){ ... }
  priority: 0|1|... 
  calls: 1|2|...
}

Predicates return a boolean and are run using whatever args are passed in by the publishing class. If the boolean is true, the subscriber is run.

Priority marks the order in which a subscriber is called.

calls allows you to specify how many times the subscriber is called before it is automatically removed. This is decremented each time it is called until it reaches 0 and is removed. If it has a predicate and the predicate does not match, calls is not decremented.

A Subscriber object is returned when calling Mediator.subscribe. It allows you to update options on a given subscriber, or to reference it by an id for easy removal later.

{
  id, // guid
  fn, // function
  options, // options
  context, // context for fn to be called within
  channel, // provides a pointer back to its channel
  update(options){ ...} // update the subscriber ({ fn, options, context })
}

Examples:

var mediator = new Mediator();

// Alert data when the "message" channel is published to
// Subscribe returns a "Subscriber" object
mediator.subscribe("message", function(data){ alert(data); });
mediator.publish("message", "Hello, world");

// Alert the "message" property of the object called when the predicate function returns true (The "From" property is equal to "Jack")
var predicate = function(data){ return data.From === "Jack" };
mediator.subscribe("channel", function(data){ alert(data.Message); }, { predicate: predicate });
mediator.publish("channel", { Message: "Hey!", From: "Jack" }); //alerts
mediator.publish("channel", { Message: "Hey!", From: "Audrey" }); //doesn't alert

You can remove events by passing in a channel, or a channel and the function to remove or subscriber id. If you only pass in a channel, all subscribers are removed.

// removes all methods bound directly to a channel, but not subchannels
mediator.remove("channel");

// unregisters *only* MethodFN, a named function, from "channel"
mediator.remove("channel", MethodFN);

You can call the registered functions with the Publish method, which accepts an args array:

mediator.publish("channel", "argument", "another one", { etc: true });

You can namespace your subscribing / removing / publishing as such:

mediator.subscribe("application:chat:receiveMessage", function(data){ ... });

// will call parents of the appllication:chat:receiveMessage namespace
// (that is, next it will call all subscribers of application:chat, and then
// application). It will not recursively call subchannels - only direct subscribers.
mediator.publish("application:chat:receiveMessage", "Jack Lawson", "Hey");

You can update Subscriber priority:

var sub = mediator.subscribe("application:chat", function(data){ ... });
var sub2 = mediator.subscribe("application:chat", function(data){ ... });

// have sub2 executed first
mediator.getChannel("application:chat").setPriority(sub2.id, 0);

You can update Subscriber callback, context, and/or options:

sub.update({ fn: ..., context: { }, options: { ... });

You can stop the chain of execution by calling channel.stopPropagation():

// for example, let's not post the message if the from and to are the same
mediator.subscribe("application:chat", function(data, channel){
  alert("Don't send messages to yourself!");
  channel.stopPropagation();
}, options: {
  predicate: function(data){ return data.From == data.To },
  priority: 0
});

Changes from Last Version

Version 0.9.0

• Reversed order of recursion: now calls parents instead of children channels
• Lowercase methods
• Aliases: on and bind are aliased to subscribe, and trigger and emit are bound to publish. off is an alias for remove.
• Moved tests to mocha from jasmine
• Supports AMD, requirejs, and browser loading
• Lots of cleanup around extra variables, and jslinted
• Published to NPM under "mediator-js"
• Added travis-ci build

Version 0.6.1

• Cleaned up some typos
• Save pointer to channel within subscription
• Save namespace in channel
• Fixed bugs in SetPriority

Version 0.6.0

• Added ability to stop the chain of calls using c.stopPropagation()

Version 0.5.0

• Added ability to access and update subscribing objects
  • Subscribers now have a unique ID and can be queried by id or by function
  • Subscriber class can have its function, context, or options updated
  • Subscriber priority can be updated post-addition
  • Channels made public by Mediator.GetChannel
  • Added a little performance test

Version 0.4.2

• Added Priority to calls, allowing you to set callback index

Version 0.4.1

• Minor internal updates

Version 0.4.0

• Predicate no longer acts as a channel and is moved to an options object at the end of the subcription call.
• Signatures changed; context moved to the end of subscriptions
• Namespacing for subscription binding

License

This class and its accompanying README and are MIT licensed.

In Closing

Have fun, and please submit suggestions and improvements! You can leave any issues here, or contact me at (@ajacksified).