Write CouchDB Changes Listeners. Easy.

var changes = require("CouchDBChanges");
changes.follow("database", function(change) {
   // do whatever you want with the change.
}, { url: "http://127.0.0.1:5984/database/"});

Wow, easy!

CouchDB, The Definitive Guide has a chapter on the Changes feed.

Wha?

CouchDB has this amazing feature called the Changes Feed. Think of git log for your database. Theres all sorts of awesome you can do with this. For example, have a database called outbox and connect a CouchDB changes listener to it and whenever your application creates a new document, say

{
    "from": "[email protected]",
    "to": "[email protected]",
    "subject": "Hey there!",
    "body": "I think you get the idea"
}

the changes listener then gets notified right when the document gets created, but asynchronously from your application and send the email that is described. When the email is sent, it can write back a new field

"status": "sent"

or, if anything went wrong:

"status": "error",
"error_message": "that email address is bogus you twat!"

So yeah, quick example, but theres tons of things you can do with this. We should collect nice examples, but for now you can check out https://github.com/janl/couchdb-external-CreateUserDatabase.

API

follow(database, change_cb, follow_options, changes_options)

database: (string) name of the database
change_cb: (callable) function to call for each change
follow_options: (object) configurations for following {
- persistent_since: (bool) false whether or not to persist the latest
  seq_id from the server. This allows us to avoid processing a
  change more than once.
  }
changes_options: (object) parameters for the follow library.