A mechanism for dispatching notifications within a Node.js program.
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README.md

Notifications

Notifications provides an architecture for broadcasting notifications within a Node.js application.

Notifications builds on Node's powerful concepts of events, and introduces an more decoupled approach. In order to receive events from an object, the listener must first obtain a reference to the emitting object in order to register as a listener. This coupling of two objects can be undesirable, especially when when it would join two otherwise independent subsystems.

For these scenarios, a broadcast mechanism is introduced in which objects post notifications to a notification center, which dispatches them to any registered observers.

Installation

$ npm install notifications

Usage

Register an Observer

Register an observer function with the notification center. Whenever a notification with the given name is posted, the function will be called. The notif passed as an argument to the function has object and info properties which contain related information.

notifications.on('users.new', function(notif) {
  var user = notif.object;
  if (notif.info.lang == 'en') {
    email.send({ to: user.email }, 'Welcome ' + user.firstName + '!');
  } else {
    // localize emails!
  }
});

Post a Notification

When an interesting event occurs in the application, post a notification to the notification center. In this example, a notification is posted whenever a new user account is created. Observers implement necessary post-processing logic, such as sending welcome emails, and are fully decoupled. The web application and email delivery subsystems remain discreet components.

app.post('/users', function(req, res) {
  // create a new user record in database
  var user = new User(...);
  user.save(function(err) {
    // user record saved, post a notification
    // observers will be notified, triggering welcome email, etc.
    notifications.post('users.new', user, { language: 'en' });
    res.redirect('/');
  });
});

NotificationCenter Instances

A default NotificationCenter is the main export of the notifications module. This instance is shared within the application, making it convenient to broadcast notifications to disparate subsystems. This is the recommended way of using notifications.

If desired, separate NotificationCenter instances can be created as well.

var nc = new notifications.NotificationCenter();

Notifications are only dispatched to observers registered with the NotificationCenter they are posted to. Having separate NotificationCenter instances allows notifications to be contained within subsystems of the application.

Tests

$ npm install
$ make test

Build Status

Credits

This module is inspired by, and patterned closely after, the NSNotificationCenter class provided within Cocoa's Foundation Framework.

License

(The MIT License)

Copyright (c) 2011 Jared Hanson

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.