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NodeJS

Question : Why You should use Node JS?
Answer : Following are the major factor influencing the use of the NodeJS
Popularity : The popularity can be important factor, as it has more user base and hence solution 
of any common problem faced by developer can found easily online, without any professional help.

JavaScript at all levels of the stack : A common language for frontend and backend offers several potential benefits:

  • The same programming staff can work on both ends of the wire
  • Code can be migrated between server and client more easily
  • Common data formats (JSON) exist between server and client
  • Common software tools exist for server and client
  • Common testing or quality reporting tools for server and client
  • When writing web applications, view templates can be used on both sides


Leveraging Google's investment in V8 Engine.

Leaner, asynchronous, event-driven model


Microservice architecture


Question : example of node JS code?
Answer : 
const fs = require('fs');
const util = require('util');
const fs_readdir = util.promisify(fs.readdir);

( async () => {
    const files = await fs_readdir('.');
    for(let file of files ){
        console.log(file);
    }

})();

Question :  Example to read the content from the command line
Answer  : 
code : 
console.log(process.argv[2] ? process.argv[2] : 'No Arguments passed');

command line : 
/usr/local/bin/node /Users/vcmishra/central-api/db> test.js hello

Question : create a basic server?
Answer : 

const http = require('http');
http.createServer((req,res)=>{
    res.writeHead(200, {'Content-Type': 'text/plain'});
    res.end('Hello, World!\n');

}).listen(1234,'127.0.0.1');

Question : Is require a async or sync?
Answer : sync.

Question : Give example of module.exports
Answer :
File 1 : the methods are created
module.exports.hello = ()=>{
    console.log('hello');
};

module.exports.hi = ()=>{
    console.log('hi');
};

File 2 : it is imported and used
const greetUtil = require('./test');
greetUtil.hello();
greetUtil.hi();

The function can directly called if imported this way

const hello = require('./test').hello;
const hi = require('./test').hi;
hello();
hi();


or alternatively can be called like as follow
require('./test').hello()
require('./test').hi()

Another way is

File 1 :
module.exports = {
    hello: () => {
        console.log('hello');
    },
    hi: () => {
        console.log('hi');
    }
};

File 2 :
There may not be needing any change, but alternativly using the es6 destrcutring you can also use as follows :

const { hello, hi } = require('./test');
hi();
hello();


Another example using destructuring
File 1
exports.util = {
    hello: () => {
        console.log('hello');
    },

    hi: () => {
        console.log('hi');
    }
};


exports.autil = {
    hello: () => {
        console.log('a hello');
    },

    hi: () => {
        console.log('a hi');
    }
};


File 2 :
const { hello, hi } = require('./test').util;
const { hello : aHello  ,  hi : aHi } = require('./test').autil;

hi();
hello();

aHi();
aHello();

Pay attention to the second line where, we are renaming the hello and hi from the autil to avoid the conflict between previously imported hi and hello from util.








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