Express.js Middleware are different types of functions that are invoked by the Express.js routing layer before the final request handler. As the name specified, Middleware appears in the middle between an initial request and final intended route. In stack, middleware functions are always invoked in the order in which they are added.
Middleware is commonly used to perform tasks like body parsing for URL-encoded or JSON requests, cookie parsing for basic cookie handling, or even building JavaScript modules on the fly.

What is a Middleware function

Middleware functions are the functions that access to the request and response object (req, res) in request-response cycle.
A middleware function can perform the following tasks:
• It can execute any code.
• It can make changes to the request and the response objects.
• It can end the request-response cycle.
• It can call the next middleware function in the stack.

Express.js Middleware

Following is a list of possibly used middleware in Express.js app:
• Application-level middleware
• Router-level middleware
• Error-handling middleware
• Built-in middleware
• Third-party middleware
Let’s take an example to understand what middleware is and how it works.
Let’s take the most basic Express.js app:

File: simple_express.js

1. var express = require('express'); 
2. var app = express(); 
3. 
4. app.get('/', function(req, res) { 
5. res.send('Welcome to tecklearn!'); 
6. }); 
7. app.get('/help', function(req, res) { 
8. res.send('How can I help You?'); 
9. }); 
10. var server = app.listen(8000, function () { 
11. var host = server.address().address 
12. var port = server.address().port 
13. console.log("Example app listening at http://%s:%s", host, port) 
14. })

You see that server is listening.
Now, you can see the result generated by server on the local host http://127.0.0.1:8000
Let’s see the next page: http://127.0.0.1:8000/help

Output:

n 21

Note: You see that the command prompt is not changed. Means, it is not showing any record of the GET request although a GET request is processed in the http://127.0.0.1:8000/help page.

Use of Express.js Middleware

If you want to record every time you a get a request then you can use a middleware.
See this example:

File: simple_middleware.js

1. var express = require('express'); 
2. var app = express(); 
3. app.use(function(req, res, next) { 
4. console.log('%s %s', req.method, req.url); 
5. next(); 
6. }); 
7. app.get('/', function(req, res, next) { 
8. res.send('Welcome to tecklearn!'); 
9. }); 
10. app.get('/help', function(req, res, next) { 
11. res.send('How can I help you?'); 
12. }); 
13. var server = app.listen(8000, function () { 
14. var host = server.address().address 
15. var port = server.address().port 
16. console.log("Example app listening at http://%s:%s", host, port) 
17. })

You see that server is listening.
Now, you can see the result generated by server on the local host http://127.0.0.1:8000

Note: In the above example next() middleware is used.

Middleware example explanation

• In the above middleware example a new function is used to invoke with every request via app.use().
• Middleware is a function, just like route handlers and invoked also in the similar manner.
• You can add more middlewares above or below using the same API.

Express.js Scaffolding

What is scaffolding

Scaffolding is a technique that is supported by some MVC frameworks.
It is mainly supported by the following frameworks:
Ruby on Rails,OutSystems Platform, Express Framework, Play framework, Django, MonoRail, Brail, Symfony, Laravel, CodeIgniter, Yii, CakePHP, Phalcon PHP, Model-Glue, PRADO, Grails, Catalyst, Seam Framework, Spring Roo, ASP.NET etc.
Scaffolding facilitates the programmers to specify how the application data may be used. This specification is used by the frameworks with predefined code templates, to generate the final code that the application can use for CRUD operations (create, read, update and delete database entries).

Express.js Scaffold

An Express.js scaffold supports candy and more web projects based on Node.js.

Install scaffold

Execute the following command to install scaffold.
1. npm install express-scaffold

After this step, execute the following command to install express generator:
1. npm install -g express-generator
Now, you can use express to scaffold a web-app.

Let’s take an example:

First create a directory named myapp. Create a file named app.js in the myapp directory having the following code:

1. var express = require('express'); 
2. var app = express(); 
3. app.get('/', function (req, res) { 
4. res.send('Welcome to tecklearn!'); 
5. }); 
6. app.listen(8000, function () { 
7. console.log('Example app listening on port 8000!'); 
8. });

Open Node.js command prompt, go to myapp and run npm init command (In my case, I have created myapp folder on desktop)
Fill the entries and press enter.
It will create a package.json file in myapp folder and the data is shown in JSON format.

n 22

Output:

n 23

So, this brings us to the end of blog. This Tecklearn ‘Scaffolding and Middleware in ExpressJS’ blog helps you with commonly asked questions if you are looking out for a job in NodeJS Programming. If you wish to learn NodeJS and build a career in NodeJS Programming domain, then check out our interactive, Node.js Training, that comes with 24*7 support to guide you throughout your learning period.

Node.js Training

About the Course

Tecklearn’s Node.js certification training course familiarizes you with the fundamental concepts of Node.js and provides hands-on experience in building applications efficiently using JavaScript. It helps you to learn how to develop scalable web applications using Express Framework and deploy them using Nginx. You will learn how to build applications backed by MongoDB and gain in-depth knowledge of REST APIs, implement testing, build applications using microservices architecture and write a real-time chat application using Socket IO. Accelerate your career as a Node.js developer by enrolling into this Node.js training.

Why Should you take Node.js Training?

• As per Indeed.com data, the average salary of Node.js developer is about $115000 USD per annum.
• IBM, LinkedIn, Microsoft, GoDaddy, Groupon, Netflix, PayPal, SAP have adopted Node.js – ITJungle.com
• There are numerous job opportunities for Node.js developers worldwide. The job market and popularity of Node.js is constantly growing over the past few years.

What you will Learn in this Course?

Introduction to Node.js

• What is Node.js?
• Why Node.js?
• Installing NodeJS
• Node in-built packages (buffer, fs, http, os, path, util, url)
• Node.js Modules
• Import your own Package
• Node Package Manager (NPM)
• Local and Global Packages

File System Module and Express.js

. File System Module
• Operations associated with File System Module
• JSON Data
• Http Server and Client
• Sending and receiving events with Event Emitters
• Express Framework
• Run a Web Server using Express Framework
• Routes
• Deploy application using PM2 and Nginx

Work with shrink-wrap to lock the node module versions

• What is shrink-wrap
• Working with npmvet
• Working with outdated command
• Install NPM Shrinkwrap

Learn asynchronous programming

• Asynchronous basics
• Call-back functions
• Working with Promises
• Advance promises
• Using Request module to make api calls
• Asynchronous Commands

Integration with MongoDB and Email Servers

• Introduction to NoSQL Databases and MongoDB
• Installation of MongoDB on Windows
• Installation of Database GUI Viewer
• Inserting Documents
• Querying, Updating and Deleting Documents
• Connect MongoDB and Node.js Application
• Exploring SendGrid
• Sending emails through Node.js application using SendGrid

REST APIs and GraphQL

• REST API
• REST API in Express
• Postman
• MongoDB Driver API
• Express Router
• Mongoose API
• GraphQL
• GraphQL Playground

Building Node.js Applications using ES6

• ES6 variables
• Functions with ES6
• Import and Export withES6
• Async/Await
• Introduction to Babel
• Rest API with ES6
• Browsing HTTP Requests with Fetch
• Processing Query String
• Creating API using ES6
• Building Dashboard API
• Creating dashboard UI with EJS
• ES6 Aside: Default Function Parameters
• Data Validation and Sanitization

User Authentication and Application Security

• Authentication
• Types of Authentication
• Session Vs Tokens
• JSON Web Tokens
• Bcrypt
• Node-local storage

Understand Buffers, Streams, and Events

• Using buffers for binary data
• Flowing vs. non-flowing streams
• Streaming I/O from files and other sources
• Processing streams asynchronously
• File System and Security

Build chat application using Socket.io

• Getting Started
• Adding Socket.io To Your App
• Exploring the Front-end
• Sending Live Data Back & Forth
• Creating the Front-end UI
• Showing Messages In App
• Working with Time
• Timestamps
• Show Message Time In Chat App
• Chat application Project

Microservices Application

• Why Microservices?
• What is Microservices?
• Why Docker?
• What is Docker?
• Terminologies in Docker
• Child Processes
• Types of child process

233