Express and Node JS Interview Questions

Node JS Interview Questions with Express Download Node JS Interview Questions with Express PDF

Node JS Interview Questions with Express

Following are the steps used to set up an express JS application: –

  1. A folder with the same name as the project name is created.
  2. A file named package.json is created inside the folder created.
  3. “npm install” command is run on the command prompt. It installs all the libraries present in package.json.
  4. A file named server.js is created.
  5. “Router” file is created inside the package which consists of a folder named index.js.
  6. “App” is created inside the package which has the index.html file.

This way, an express JS application is set up.

Some of the main features of Express JS are listed below: –

  • It is used for setting up middlewares so as to provide a response to the HTTP or RESTful requests.
  • With the help of express JS, the routing table can be defined for performing various HTTP operations.
  • It is also used for dynamically rendering HTML pages which are based on passing arguments to the templates.
  • It provides each and every feature which is provided by core Node JS.
  • The performance of Express JS is adequate due to the presence of a thin layer prepared by the Express JS.
  • It is used for organizing the web applications into the MVC architecture.
  • Everything from routes to rendering view and performing HTTP requests can be managed by Express JS.

Following are the list of few new Features introduced in ES6

  • const and let keywords
  • Array helper functions like map, forEach, filter, find, every, some, reduce
  • Arrow functions
  • Classes and enhanced object literals
  • Template strings
  • Default function arguments
  • Rest and spread operators
  • Promises
  • Modules
  • Multi-line Strings
  • Destructuring Assignment

CORS stands for Cross-Origin Resource Sharing. It a is a mechanism that uses additional HTTP headers to tell a browser to let a web application running at one origin (domain) have permission to access selected resources from a server at a different origin.

Use below code to enable CORS on NodeJS

app.use(function(req, res, next) {
  res.header("Access-Control-Allow-Origin", "*");
  res.header("Access-Control-Allow-Headers", "Origin, X-Requested-With, Content-Type, Accept");
  next();
});

Use node-uuid package to generate unique UUIDs/ guid in Node Js. Below code demonstrates how to generate it.

var uuid = require('node-uuid');

// Generate a v1 (time-based) id 
uuid.v1(); 

// Generate a v4 (random) id 
uuid.v4(); 

Express JS is an application framework which is light-weighted node JS. A number of flexible, useful and important features are provided by this JavaScript framework for the development of mobile as well as web applications with the help of node JS.

Run below command on the terminal to set default node version along multiple installed versions of node. You can list all install versions of the node by running nvm ls

nvm alias default v7.3.0
An event is an action or occurrence recognized by software/app that is handled by event handler by writing a code that will be executed when the event fired.
Mouse move, Click, file copied or deleted are some examples of events.
In Node Js there are two types of events.
1)System Events: The event that comes from the C++ side.
2)Custom Events: Custom events are user-defined events.
In Node Js processes are single threaded, to supports concurrency it uses events and callbacks. An event loop is a mechanism that allows Node.js to perform non-blocking I/O operations.