postal.js/example/node/collectors/tweet-count.js

var _ = require('underscore'),
	TweetCount = function(namespace) {
		this.namespace = namespace;

		this.events = {};

	    this.tweeters = { list: [], registry: {} };

	    this.lastStats = undefined;
	};

TweetCount.prototype = {
	init: function() {
		this.tweeters   = { list: [], registry: {} };
		this.lastStats = undefined;
	},
	on: function( eventName, callback ) {
		if( !this.events[ eventName ] ) {
			this.events[ eventName ] = [];
		}
		this.events[ eventName ].push( callback );
		return function() {
			this.events[ eventName ] = _.without( this.events[ eventName ], callback );
		}.bind( this );
	},
	raiseEvent: function( eventName, data ) {
		if( this.events[ eventName ] ) {
			this.events[ eventName ].forEach( function( callback ){
				callback.call( this, data );
			});
		}
	},
	processNewTweets: function(tweets) {
		tweets.forEach(function(tweet){
			this.processTweetCount(tweet);
		}, this);
		this.lastStats = { type: "TweetCount", tweeters: this.tweeters.list };
		this.raiseEvent( this.namespace, this.lastStats );
	},
	processTweetCount : function(tweet) {
		if(tweet.from_user) {
			if(!this.tweeters.registry[tweet.from_user]) {
				var obj = {user: tweet.from_user, count: 0, image: tweet.profile_image_url};
				this.tweeters.registry[tweet.from_user] = obj;
				this.tweeters.list.push(obj);
			}
			this.tweeters.registry[tweet.from_user].count++;
		}
	}
};

module.exports = TweetCount;