Express JS Interview Questions and Answers

Express JS Interview Questions and Answers

On January 17, 2022, Posted by , In Interview Questions, With Comments Off on Express JS Interview Questions and Answers

Q29 – What is express.js?

A – Express.js is a lightweight, flexible Node.js framework that is used for building server-side web applications. 

Q30 – Give some features of express?

A – Following are the features of express:

  • Express can be used to build single-page as well as multi-page applications. Moreover, it can also be used to build hybrid applications and APIs.
  • Routing can be performed easily using express
  • Express is single-threaded and asynchronous.
  • Useful middlewares can be defined using express for handling HTTP or RESTful requests.
  • Express can be used with both RDBMS and NoSQL databases.

Q31 – Differentiate between Node.js.js and express.js.

A – Following are the differences between Node.js and Express.js:

  • Node.js is a JavaScript environment while Express.js is a Node.js framework. 
  • Node.js is built using Google Chrome’s V8 engine while Express.js is built on Node.js.
  • Express.js provides features such as routing and middlewares but no such features are available in Node.js.

Q32 – What is a middleware function?

A – A function that has access to the request object, response object, and next function is called a middleware function.

Q33 – What is the use of the middleware function?

A – Middleware function is used to:

  • Execute any kind of code
  • to update the response or request objects.
  • to call the next middleware

Q34  – What are the types of middlewares in express?

A – Types of middlewares in express are:

  • Router-level middleware
  • Built-in middleware
  • Application-level middleware
  • Error-handling middleware
  • Third-party middleware

Q35 – What is a route handler?

A – A router handler in the express is a middleware function that executes when a matching request to its specified route is found.

Q36 – Name the parameters of a route handler.

A – The parameters of a route handler are:

  • request object
  • response object
  • next() function

Q37 – What is the usage of the next() function?

A – The next() function is an optional parameter of a route handler. It is used to pass the execution to the next route.

Q38 – Observe the following route handler.

app.get(‘/user/:id’, function (req, res, next) {


How to access “id” in this route handler?

A – To access “id” from the router, we can use the “params” property of the request object. Observe the following code.

Q39 – What is the use of express.json()?

A – It is an express in-built middleware function that is used to parse the incoming requests with JSON data. 

Q40 – What is CORS?

A – CORS stands for Cross-origin Resource Sharing. It is used to skip the same-origin policy so that AJAX requests can access the resources from any outside host.

Q41 – How to enable CORS in an express application?

A – To enable CORS, first install it using the following command.

npm install cors

And then, import the CORS to use it as a middleware.


Q42 – How to handle errors using middleware?

A – A middleware function in express can have an additional parameter, named “err”. The “err” holds the information regarding the error. This parameter should be the first parameter for the middleware.  

Q43 – Give the ways for configuring properties in express?

A – There are two ways for configuring properties in the express.

  • By using process.env
  • By using Requirejs

Q44 – Explain the cookie.

A – Cookie is the information of a user’s action that is sent from the server side and stored on the client side.

Q45 – What is the purpose of using cookies?

A – The purpose of using cookies are:

  • Tracking user
  • Managing session
  • Personalization

Q46 – Which package is needed to use cookies in express?

A – The cookie parser is needed to use cookies in the express.

Q47 – What is pug?

A – Pug is the most popular templating engine that is used with express.

Q48 – Explain scaffolding.

A – In simple terms, scaffolding is a tool that is used to create a structure of an express application.

Q49 – Name the types of Http requests.

A – Following are the types of Http requests.

  • GET
  • POST
  • PUT
  • HEAD

Q50 – What is the difference between PUT and PATCH?

A – The PUT request modifies the entire resource while the PATCH request only modifies the specific part of the resource.

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