The document provides an overview of Express JS, a popular web application framework for Node.js. It discusses key Express concepts like routing, middleware, configuration and error handling. It also covers REST and RESTful web services. Examples are provided to demonstrate basic routing and creating a simple "Hello World" Express app.

1. EXPRESS JS
Prepared By:
Mrs. Bareen Shaikh
Assistant Professor
Computer Science
MIT ACSC Alandi(D)
Pune

2. Express JS content
▪ 9.1 REST
▪ 9.2 Introduction to Express JS
▪ 9.3 Routing, Responding
▪ 9.4 Configuration
▪ 9.5Views
▪ 9.6 Receiving Data
▪ 9.7 Error Handling

3. REST
▪ REST stands for REpresentational StateTransfer.
▪ REST was first introduced by Roy Fielding in 2000.
▪ REST is web standards based architecture using
HTTP Protocol.
▪ It revolves around resource where every
component is a resource .
▪ A resource is accessed by a common interface using
HTTP standard methods.
▪ A REST Server simply provides access to resources
and REST client accesses and modifies the
resources using HTTP protocol.
▪ REST uses various representation to represent a
resource like text, JSON, XML but JSON is the most
popular one.

4. RESTful Web Services
▪ Web services based on REST Architecture are known as
RESTful web services.
▪ These webservices uses HTTP methods to implement
the concept of REST architecture.
▪ A RESTful web service usually defines a URI, Uniform
Resource Identifier a service, which provides resource
representation such as JSON and set of HTTP Methods.
▪ HTTP methods
▪ Following four HTTP methods are commonly used in
REST based architecture.
 GET −This is used to provide a read only access to a resource.
 PUT −This is used to create a new resource.
 DELETE −This is used to remove a resource.
 POST −This is used to update a existing resource or create a
new resource.

5. RESTful Architecture(Example
of Customer Service)

6. RESTful Architecture
Overview

7. Introduction to Express JS
▪ Express was developed byTJ Holowaychuk .
▪ Express is a minimal and flexible Node.js web
application framework .
▪ It provides a robust set of features to develop web
and mobile applications.
▪ Following are the core features of Express
framework:
 Allows to set up middlewares to respond to HTTP
Requests.
 Defines a routing table which is used to perform different
action based on HTTP Method and URL.
 Allows to dynamically render HTML Pages based on
passing arguments to templates.

8. Introduction to Express JS
▪ It is maintained by the Node.js foundation and
numerous open source contributors.
▪ It facilitates a rapid development of Node based
Web applications.
▪ Express provides a minimal interface to build
our applications.
▪ It provides us the tools that are required to build
our app.
▪ It is flexible as there are numerous modules
available on npm, which can be directly plugged
into Express.

9. Middleware
▪ Express is a routing and middleware web
framework that has minimal functionality of its
own.
▪ An Express application is essentially a series of
middleware function calls.
▪ Middleware functions are functions that have
access to the request object (req), the response
object (res), and the next middleware function
in the application’s request-response cycle.
▪ The next middleware function is commonly
denoted by a variable named next.

10. Using Middleware
▪ Middleware functions can perform the following tasks:
 Execute any code.
 Make changes to the request and the response objects.
 End the request-response cycle.
 Call the next middleware function in the stack.
 If the current middleware function does not end the request-
response cycle, it must call next() to pass control to the next
middleware function. Otherwise, the request will be left
hanging.
▪ An Express application can use the following types of
middleware:
 Application-level middleware
 Router-level middleware
 Error-handling middleware
 Built-in middleware
 Third-party middleware

11. Installing Express
▪ Firstly, install the Express framework using npm so that it can be
used to create web application using node terminal.
 $ npm install express --save
▪ Above command saves installation locally in node_modules
directory and creates a directory express inside node_modules.
▪ Following more modules should be install along with express:
 body-parser -This is a node.js middleware for handling JSON,
Raw,Text and URL encoded form data.
 $ npm install body-parser --save
 cookie-parser - Parse Cookie header and populate req.cookies
with an object keyed by the cookie names.
 $ npm install cookie-parser --save
 multer -This is a node.js middleware for handling
multipart/form-data.
 $ npm install multer --save

12. Hello World Example
var express = require('express');
var app = express();
app.get('/', function(req, res){
res.send("Hello world!");
});
app.listen(4000);
 Save the file, in terminal type the following.
$node hello.js
 This will start the server.
 Open browser and open http://localhost:4000.

13. Explanation of example
▪ app.get(route, callback)
 This function tells what to do when a get request at
the given route is called.
 Callback function has 2 parameters, request(req)
and response(res).
 The request object(req) represents the HTTP request
and has properties for the request query string,
parameters, body, HTTP headers, etc.
 The response object represents the HTTP response
that the Express app sends when it receives an HTTP
request.

14. Explanation of example
▪ res.send()
 send() function takes an object as input
 It sends this to the requesting client.
 In above example sending the string "HelloWorld!".
▪ app.listen(port, [host], [backlog], [callback]])
 listen() binds and listens for connections on the
specified host and port.
 port is the required parameter here, remaining
parameter are optional.
 backlog is the maximum number of queued pending
connections.
 callback is an asynchronous function that is called when
the server starts listening for requests.

15. ExpressJS Routing
▪ Following function is used to define routes for an
application
 app.method(path, handler)
▪ METHOD can be applied any one of the HTTP
verbs – get, set, put, delete.
▪ An alternate method also exists, which
executes independent of the request type.
▪ Path is the route at which request will run.
▪ Handler is a callback function that executes
when a matching request type is found on the
relevant route.

16. ExpressJS Routing Example
var express = require('express');
var app = express();
app.get('/', function(req, res){
res.send("Hello world!");
});
app.get('/hello', function(req, res){
res.send(“routed to /hello page");
});
app.listen(4000);
 Open browser and open localhost:4000/hello
 The server receives a get request at route "/hello”
 Express app executes the callback function attached to this
route

17. ExpressJS Routing Example
var express = require('express');
var app = express();
app.get('/', function(req, res){
res.send("Hello world!");
});
var server = app.listen(4000, function () {
var host = server.address().address
var port = server.address().port
console.log("%s : %s", host, port)
}) ;