Top Express.js Interview Questions and Answers

By | February 9, 2017
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This Web Development Tutorial is last in series of MEAN Stack Interview Questions and Asnwers series covering ExpressJS. Previously, we have covered all other areas including AngularJS, AngularJS 2, NodeJS and MongoDB. You can follow the below link to get updates about all MEAN Stack development articles and tutorials covered so far as well as published in future.

MEAN Stack ExpressExpress.js is another famous JavaScript Framework that gained a lot more popularity in recent years. We will follow the same strategy to explore all various topics by following Interview Question and Answer pattern.

Express.js Interview Questions PDF version will be available later for download.

Express.js Interview Questions List

What is Express.js? What are core features of Express framework?

What is Express.js?

Express.js is a light-weight node.js based web application framework. This JavaScript framework provides a number of flexible and useful feature in order to develop mobile as well as web application using NodeJS.

ExpressJS Features:

Following are some of the core features of Express framework −

  • Set up middlewares in order to respond to HTTP/RESTful Requests.
  • It is possible to defines a routing table in order to perform different HTTP operations.
  • Dynamically renders HTML Pages based on passing arguments to templates.
  • Provides all the feature provides by core Node.js.
  • Express prepare a thin layer, therefore, the performance is adequate.
  • Organize the web application into an MVC architecture.
  • Manages everything from routes to rendering view and preforming HTTP request.

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How to setup an Express.js App?

We can follow the below step by step approach to set up an Application using ExpressJS Framework.

  • Create a folder with the same name as Project name.
  • Inside the folder create a file called package.json.
  • Open command prompt on the project folder and run following command.
    This will install all the libraries defined in package.json inside dependencies{} and the libraries are installed in node_modules folder.
  • Create a file called server.js.
  • Create a folder called ‘routes’ inside the project folder.
  • Create a file inside ‘routes’ folder called index.js.
  • Create a folder called ‘app’ inside the project folder and create a file inside ‘app’ folder called ‘index.html’.ExpressJS Setup Tutorial
  • Create a index.html file.
  • Open command prompt on the project folder and run following command.
    The output would be
  • Now open a browser with link http://localhost:3000, the output would be:ExpressJS App Tutorial

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How to config Angular 2.0 Frontend in Express.js Application?

With the Angular 2.0 the MEAN stack has a huge changes. These are the following steps to create an application using MEAN stack.

  • Install Node.js.
  • Create an express application using express generator.
  • Use the view engine as ejs, therefore, install ejs.
  • Set view engine in app.js.
  • Set the static folder.
  • Create the config file inside public folder following the Getting started from angular.io.
    package.json

    tsconfig.json

    typings.json
    system.config.js
  • Now run ‘npm install’ command to install all the necessary dependencies.
  • Change the ‘views/index.html’ folder with the following code.
  • Create an app.component.
  • Add the template.
  • Create Angular App module in ‘public/app/app.module.ts’.
  • Now on the browser it would look like:Getting Started ExpressJS
  • Similarly add other angular module to the angular app.

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Explain Routing in Express.js in details?

  • Create a file called routes.js  containing all the routes of the application.
  • Create a file called MemberController.js.
  • Create a file called MemberService.js and DatabaseService.js would be created.
  • In server.js add the following code:
  • Now any  of the route defined in routes.js can be accessed.

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Explain Logging in Express.js? Give a practical example to demonstrate?

With Express 4.0, the application can be generated using express-generator and it includes morgan as the logger:

  • Create express app using express generator.
  • The middleware in app.js is already added.
  • Create the local middleware.
  • Otherwise, If logging is need to be added to a log file.
    Add fs to app.js
    Add the file
    Create the middleware
  • Make sure logging will be enabled only in development environment.
  • Now if we run from the browser we can see that every request is being logged.

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How to config properties in Express Application?

In an ExpressJS Application, we can config properties in following two ways:

With Process.ENV?

  • Create a file with name ‘.env’ inside the project folder.ExpressJS Config Properties
  • Add all the properties in ‘.env’ file.Environment File in ExpressJS
  • In server.js any of the properties can be used as:

With RequireJs?

  • Create a file called  ‘config.json’ inside a folder called ‘config’ inside the project folder.
  • Add config properties in config.json.
  • Use require to access the config.json file.

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How to allow CORS in ExpressJS? Explain with an example.

In order to allow CORS in Express.js,  add the following code in server.js:

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How to redirect 404 errors to a page in ExpressJS?

In server.js add the following code to redirect 404 errors back to a page in our ExpressJS App:

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Explain Error Handling in Express.js using an example?

From Express 4.0 Error handling is much easier. The steps are as following:

  • Create an express.js application and as there is no built-in middleware like errorhandler in express 4.0, therefore, the middleware need to be either installed or need to create a custom one.

Create a Middleware:

  • Create a middleware as following:

Install Error Handler Middleware:

  • Install errorhandler.
  • Create a variable.
  • Use the middleware as following:

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How to implement File uploading and downloading with Express?

Below we have explained the process to upload as well as download a file with ExpressJS App.

Upload File in Express.js:

  • Install formidable.
  • Add the following code in server.js in order to upload a file.
  • Update the index.html as following:
  • On Browser run ‘http://localhost:3000’.

Download File in Express.js:

  • Add the following code in server.js.

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How to enable debugging in express app?

In different Operating Systems, we have following commands:

On Linux the command would be as follows:

On Windows the command would be:

From Webstrome IDE

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How to implement JWT authentication in Express app ? Explain with example.

  • Create a folder called ‘keys’ inside project folder.
  • Install some dependencies as following:
  • Add the login router routes/index.js
  • Use the token in application

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That is all we have about Express.js Interview Questions and Answers. Next we will come up with more related Web Development related Interview Questions and Answers. You can follow the below given other technical interview questions and answers to improve your technical skills.

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