02 | Understanding Module Design Pattern 03 | Express.js

Ahmed Assaf | Senior Software Engineer

Setting Expectations

Target Audience Web Developers Web Designers Developers with experience using other service side languages such as

PHP, ASP.NET, Python, Ruby etc.

Module Overview Exports a Namespace Exports a Function Exports a Higher Order Function Exports a Constructor Exports a Singleton Extends a Global Object Applies a Monkey Patch

Module Design Patterns Modules are still JavaScript Possess many of the challenges of pre-ES6 Javascript Design Patterns to help with

Encapsulation Stable Interface

Exports a Namespace

Exports a Namespace Module returns an object Object contains properties and functions Calling code can refer to properties and execute functions

Simply return an object with whatever properties and functions the calling code should have access to

//private module stuff can happen here

//then return an objectmodule.exports = { property1: 'value', property2: 'value', function1: function(){ … } function2: function(){ … }}

Core 'fs' Node module returns an objectreadFile and ReadStream are functions of the returned objectBoth are accessible from this calling functionAnalogous to static classes and members in other languages

var fs = require('fs');

fs.readFile('./file.txt', function(err, data) { console.log("readFile contents: '%s'", data);});

new fs.ReadStream('./file.txt').on('data', function(data) { console.log("ReadStream contents: '%s'", data);});

Exports a Function

Exports a Function Factory function Gives you instancing since all variables are encased in a closure Closure is run for each require() Revealing Module Pattern you may have used in client side JavaScript ProTip

If you don’t need instancing – export a namespace If you need instancing – export a constructor

module.exports = function(options) {options = options || {};var loggingLevel = options.loggingLevel || 1;

function logMessage(logLevel, message) {if(logLevel <= loggingLevel) {

console.log(message);}

}return { log: logMessage };

}

DEMO

Exports a Higher Order Function

Exports a Higher Order Function Like the former, but also receives a function that affects the behavior of the function it returns Express middleware is a great example - functions are provided and the middleware function is

returned

Chaining is possible with the app object because the middleware functions each return it.

var app = require('express')();

app.use('/route1', function(res, req, next) { //do something next();});

app.use('/route2', function(res, req, next) { //do something next();});

Exports a Constructor

Exports a Constructor Constructor function creates instance Prototype used to define behavior Caller creates instance with new keyword Multi instance

DEMO

Exports a Singleton

Exports a Singleton Instantiates object before returning it Causes all calling modules to share a single object instance

When an object is instantiated before it's returned, it acts as a singleton.

function Something() { …}

module.exports = new Something();

Mongoose is one example of a good use of the singleton pattern

var mongoose = require('mongoose');mongoose.connect('mongodb://localhost/test');

var Cat = mongoose.model('Cat', { name: String });

var kitty = new Cat({ name: 'Zildjian' });kitty.save(function (err) { if (err) // ... console.log('meow');});

Extends a Global Object

Extends a Global Object Modifies an existing type i.e. String Doesn’t have to export anything Makes for nice calling syntax but can be difficult to track down source in large project Frowned upon in open source packages

Applies a Monkey Patch

Applies a Monkey Patch A monkey patch is the dynamic modification of a class or object at runtime to fix a bug in

existing code Similar to previous pattern (extends a global object) but affects cached node modules

The winston logger defaults all profiling statements to the info level and you can’t changeA quick monkey patch allows you to log data out as any log level you want and replace the built in functionality without forking the code base

winston.Logger.prototype.profile = function(id) {

// Altered behvaior or winston loggers profile function

};

Summary Exports a Namespace Exports a Function Exports a Higher Order Function Exports a Constructor Exports a Singleton Extends a Global Object Applies a Monkey Patch

03 | Express.js

What is Express? Express is a minimal, open source and flexible node.js web app framework designed to make

developing websites, web apps and APIs much easier.

Why use Express?

Express helps you respond to requests with route support so that you may write responses to specific URLs.

Supports multiple templating engines to simplify generating HTML.

Installing and Using Express

Installing and Using Expressnpm install expressnpm install jade

Creating a Simple REST API

Explanation of Routes

A router maps HTTP requests to a callback. HTTP requests can be sent as GET/POST/PUT/DELETE, etc. URLs describe the location targeted. Node helps you map a HTTP GET request like:

http://localhost:8888/index To a request handler (callback)

app.get('/index', function (req, res) {});

Creating a Simple Express Applicationvar express = require('express'); var app = express();

app.get('/', function (req, res) {     res.json({message:'hooray! welcome to our api!'});});

app.listen(process.env.PORT || 8080);

DEMOCreating a simple REST API with Express Framework

DEMOUsing the express-generator package.

DEMOUsing Express for Multiple Pages with Query Parameters

Building a RESTful API for DogsResource GET PUT POST DELETE

Collection URI, such as http://api.example.com/v1/dogs/

List all the dogs

Replace all the dogs with a new collection of dogs.

Create a new dog in the collection.

Delete the entire dog collection.

Element URI, such as http://api.example.com/v1/dog/1

Get a specific dog.

Replace a dog in the collection with another dog.

Not used.Delete the dog from the collection.

DEMOUsing Express to build a RESTful API

Resources

Express Framework http://expressjs.com/ Intro to Express

http://code.tutsplus.com/tutorials/introduction-to-express--net-33367 Jade Templates http://jade-lang.com/tutorial/ JavaScript and Jade Templating

http://www.slideshare.net/wearefractal/jade-javascript-templating

Resources Using Node.js with Visual Studio Code #MVA Course By

Stacey Mulcahy | Senior Technical Evangelist Rami Sayar | Technical Evangelist

Mastering Node.js Modules #MVA Course By Chris Kinsman | Chief Architect at PushSpring

https://blog.jcoglan.com/2013/03/30/callbacks-are-imperative-promises-are-functional-nodes-biggest-missed-opportunity/

http://code.tutsplus.com/tutorials/using-nodes-event-module--net-35941 http://spin.atomicobject.com/2012/03/14/nodejs-and-asynchronous-programming-with-

promises/

Github repo: https://github.com/AhmedAssaf/NodeMVA From : https://github.com/sayar/NodeMVA