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ExpressJS-Introduction.pdf

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Bareen Shaikh

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.

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EXPRESS JS Prepared By: Mrs. Bareen Shaikh Assistant Professor Computer Science MIT ACSC Alandi(D) Pune
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
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.
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.
RESTful Architecture(Example of Customer Service)
RESTful Architecture Overview
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.
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.
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.
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
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
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.
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.
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.
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.
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
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) }) ;

More Related Content

ExpressJS-Introduction.pdf

  • 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.
  • 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) }) ;