Express and Node JS Interview Questions

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Express and Node JS Interview Questions

libuv is Cross-platform I/O abstraction library that supports asynchronous I/O based on event loops.It is written in C and released under MIT Licence.

libuv support Windows IOCP, epoll(4), kqueue(2), and Solaris event ports. Initially, it was designed for Node.js but later it is also used by other software projects.

Reference : https://en.wikipedia.org/wiki/Libuv

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.

Zlib is Cross-platform data compression library. It was written by Jean-loup Gailly and Mark Adler. In Node js, you can Zlib for Threadpool, HTTP requests, and responses compression and Memory Usage Tuning. In order to use zlib in node js, you need to install node-zlib package. After installation below is sample code to use Zlib.

var Buffer = require('buffer').Buffer;
var zlib = require('zlib');

var input = new Buffer('lorem ipsum dolor sit amet');
var compressed = zlib.deflate(input);
var output = zlib.inflate(compressed);

Further Reading https://nodejs.org/api/zlib.html

https://en.wikipedia.org/wiki/Zlib

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.
Node Js is one of the most popular and powerful server technologies today.
It allows you built the entire website only in one programming Language i.e Javascript. Node js is free and open source server technology that uses Javascript to create complete web software.It runs on various platforms like Windows, Linux, Unix, Mac OS X, etc.

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(); 

Aggregations are a set of functions that are used to manipulate the data that has been returned from a MongoDB query. In Mongoose, aggregations work as a pipeline. The aggregate function accepts the array of data transformations which are applied by data using different methods in terms of arguments.

Syntax: db.customers.aggregate([ ... aggregation steps go here ...]);

In above, aggregation is applied to data of customers.

ECMAScript is the standard on which Javascript is based on. It was created to standardize Javascript. It is commonly used for client-side scripting on the World Wide Web and used by Node Js for writing server applications and services.

Normally NodeJs reads the content of a file in non-blocking, asynchronous way. Node Js uses its fs core API to deal with files. The easiest way to read the entire content of a file in nodeJs is with fs.readFile method. Below is sample code to read a file in NodeJs asynchronously and synchronously.

Reading a file in node asynchronously/ non-blocking

var fs = require('fs'); 
fs.readFile('DATA', 'utf8', function(err, contents) {
    console.log(contents);
});
console.log('after calling readFile');

Reading a file in node asynchronously/blocking

var fs = require('fs'); 
var contents = fs.readFileSync('DATA', 'utf8');
console.log(contents);
The method or variable defined in modules cannot be directly accessible by the outer world, that means you cannot call a module member from the external file. In order to access module member, we need to export the functions or variables of modules using module.exports method.

Syntax and usage:

// greet.js
var greet=function(){
console.log("hello World");
}
module.exports=greet;

//In app.js

var greet=require('./greet.js');

greet();