Writing My First Node.js Module And Event Emitter

code-1.js

(function(){

	// Define your class.

	return( Singleton || Constructor );

})();

code-2.js

// Define our module.
(function(){

	// Counter variable.
	var counter = 0;

	// Return public API.
	return({
		countUp: function(){
			return( ++counter );
		}
	});

})();

code-3.js

// Define our module.

// Counter variable.
var counter = 0;

// Export our public API.
exports.countUp = function(){
	return( ++counter );
};

code-4.js

// Include the necessary modules.
var sys = require( "sys" );
var http = require( "http" );

// Include the Controller layer.
var controller = require( "./controller.js" );


// ---------------------------------------------------------- //
// ---------------------------------------------------------- //


// Create an instance of the HTTP server.
var server = http.createServer(
	function( request, response ){


		// Our controller is an instance of the Event Emitter. We
		// will be using this to listen to controller events. We
		// could have handled this with Success and Fail callbacks;
		// but, I wanted an excuse to experiment with the Event
		// stuff as it appears to be quite central to Node.js.


		// Bind to the "Data" event. This is the event that gets
		// emitted when the controller has data to return.
		controller.on(
			"data",
			function( data ){

				// Set the 200-OK header.
				response.writeHead(
					200,
					{ "Content-Type": "text/plain" }
				);

				// Return the response from the API request.
				response.write( JSON.stringify( data ) );

				// Close the request.
				response.end();

			}
		);


		// Bind to the "Error" event. This is the event that gets
		// triggered when a success response cannot be returned. This
		// will either be because an error occurred; or, because the
		// record request by the API cannot be found.
		//
		// NOTE: For our simple purposes, we are going to assume that
		// the errorType is simply an HTTP Status Code. This will
		// keep our logic very simple for this exploration.
		controller.on(
			"error",
			function( errorType ){

				// Set the error header (is really just an HTTP
				// status for our purposes).
				response.writeHead(
					errorType,
					{ "Content-Type": "text/plain" }
				);

				// Close the request.
				response.end();

			}
		);


		// Pass the request off to the controller.
		controller.handle( request, response );


	}
);

// Point the server to listen to the given port for incoming
// requests.
server.listen( 8080 );


// ---------------------------------------------------------- //
// ---------------------------------------------------------- //


// Write debugging information to the console to indicate that
// the server has been configured and is up and running.
sys.puts( "Server is running on 8080" );

code-5.js

// Include the event emitter class - the controller is a specialized
// instance of the event emitter and will emit the events:
//
// - data / response
// - error / errorType (HTTP Status code)
var EventEmitter = require( "events" ).EventEmitter;

// Include the Girl Service layer.
var girlService = require( "./girl-service.js" );


// ---------------------------------------------------------- //
// ---------------------------------------------------------- //


// Create an instance of our event emitter.
var controller = new EventEmitter();


// Add a handle method to the event emitter instance (controller)
// so that the HTTP server will be able to pass the request off for
// proper routing.
controller.handle = function( request, response ){

	// We are going to be looking at urls for RESTful commands.
	// These will be in the form of:
	//
	// NOTE: I am using the term RESTful in the loosest sense.
	// Really, this is just easy for illustration purposes.
	//
	// girls/get
	// girls/{id}/get
	// girls/{id}/delete
	// girls/add/{name}


	// Define our patterns.
	var patterns = {
		getAll: new RegExp( "girls/get", "i" ),
		getGirl: new RegExp( "girls/(\\d+)/get", "i" ),
		deleteGirl: new RegExp( "girls/(\\d+)/delete", "i" ),
		addGirl: new RegExp( "girls/add/([^/]+)", "i" )
	};

	// Strip off the leading and trailing slashes.
	var restUri = request.url.replace(
		new RegExp( "^/|/$", "g" ),
		""
	);


	// Loop over the patterns to see if any match.
	for (var patternKey in patterns){

		// Try to match the pattern against the URL.
		if ( match = restUri.match( patterns[ patternKey ] ) ){

			// Pass the request off to the service layer. Since
			// the service layer is performing asynchronous I/O
			// (theoretically), we need to pass it a callback so
			// that the service layer can alert us to data events
			// when they are available.

			// Build the arguments. Our last argument will always
			// be a callback for our asynchronous API. In this case,
			// the callback will be expecting an API response for a
			// successful call; OR, a null response for a record that
			// could not be found.
			var apiArguments = [function( apiResponse ){

				// Check to see if we have a valid API response.
				if (apiResponse){

					// The API request was successful - announce
					// the data event.
					controller.emit( "data", apiResponse );

				} else {

					// The API request was not successful - announce
					// the error event.
					controller.emit( "error", "404" );

				}

			}];

			// If there is a captured group in the regex pattern
			// that we used above, add it as the first argument to
			// our collection of service-layer invocation arguments.
			if (match.length > 1){

				// Prepend the captured group (an ID) to the list
				// of arguments used to invoke the service layer.
				apiArguments.unshift( match[ 1 ] );

			}

			// Invoke the service layer (remember, the last argument
			// of our invocation array is always the callback for
			// asynchronous I/O).
			girlService[ patternKey ].apply(
				girlService,
				apiArguments
			);

			// The RESTful URL can only match one pattern.
			// Since we found a match, return out of the request
			// handler as there is nothing more we can do here
			// until the data-callback is triggered.
			return;

		}

	}


	// If we have made it this far, then the incoming request did
	// not match up with any known API signature. As such, we will
	// announce (emit) a server error.
	controller.emit( "error", "500" );

};


// ---------------------------------------------------------- //
// ---------------------------------------------------------- //


// Expose the controller / event emitter. Since we are exposing
// the whole object, rather than just an API interface, we are
// redefining the entire exports value.
module.exports = controller;

code-6.js

// Create our collection of girls. This collection is keyed by the
// ID of the girl.
var girls = {};

// Keep a running auto-incrementer.
var primaryKey = 0;


// ---------------------------------------------------------- //
// ---------------------------------------------------------- //


// Now, we have to define the exteranl, public API of the module.
// Each of the methods in this API gets "exported" as part of the
// exposed object.


// All of these methods deal with data READS and WRITES. In Node,
// this kind of I/O is supposed to be asynchronous; that is, a
// method that reads or writes to storage can't return a value
// directly (as it is non-blocking... for the most part). Therefore,
// we have to pass callbacks to all of our IO methods so that our
// calling context can be *alerted* to data events.


// I am creating a noop function so I can simplify the logic
// surrounding my callbacks. With a noop() (read as No-Op), I can
// always have a reference to *a* callback.
var noop = function(){};


// I add a girl to the collection.
exports.addGirl = function( name, callback ){
	// Make sure a callback is defined.
	callback = (callback || noop);

	// Create the new girl instance.
	var girl = {
		id: ++primaryKey,
		name: name
	};

	// Add it to the collection.
	girls[ girl.id ] = girl;

	// Pass the girl to the callback (the calling context).
	callback( girl );

	// Return this object reference to allow for method chaining.
	return( this );
};


// I delete the girl with the given ID.
exports.deleteGirl = function( id, callback ){
	// Make sure a callback is defined.
	callback = (callback || noop);

	// Get the girl.
	var girl = (girls[ id ] || null);

	// If the girl exists, delete her.
	if (girl){
		delete girls[ girl.id ];
	}

	// Pass the girl to the callback (the calling context).
	callback( girl );

	// Return this object reference to allow for method chaining.
	return( this );
};


// I return the girl with the given id.
exports.getGirl = function( id, callback ){
	// Make sure a callback is defined.
	callback = (callback || noop);

	// Pass the girl to the callback (the calling context).
	callback( girls[ id ] || null );

	// Return this object reference to allow for method chaining.
	return( this );
};


// I get all the girls.
exports.getAll = function( callback ){
	// Make sure a callback is defined.
	callback = (callback || noop);

	// Create a holder for our ordered collection.
	var orderedGirls = [];

	// Loop over the primary keys to build up the collection
	// of ordered girls.
	for ( var i = 1 ; i <= primaryKey ; i++ ){

		// Check to see if a girl exists at this key.
		if (girls[ i ]){

			// Add this girl to the result in order.
			orderedGirls.push( girls[ i ] );

		}

	}

	// Pass the collection to the callback (the calling context).
	callback( orderedGirls );

	// Return this object reference to allow for method chaining.
	return( this );
};