Nodejs - ECMA Concept

ECMA Concept

-> 'let ' is an scope varible it can't be use as globle varible

-> if we'r using 'var' in place of let it will re-assign last defined value (means

    var a = 30

    var a = 30

    console.log("value of a is:"+a)

OUTPUT-

        value of a is = 30

)

if we are using 'let' inplace of var then it look like

let a=40;

let a=30;

OUTPUT

SyntaxError: Identifier 'a' has already been declared

    at wrapSafe (internal/modules/cjs/loader.js:1001:16)

    at Module._compile (internal/modules/cjs/loader.js:1049:27)

    at Object.Module._extensions..js (internal/modules/cjs/loader.js:1114:10)

    at Module.load (internal/modules/cjs/loader.js:950:32)

    at Function.Module._load (internal/modules/cjs/loader.js:790:12)

    at Function.executeUserEntryPoint [as runMain] (internal/modules/run_main.js:76:12)

    at internal/main/run_main_module.js:17:47 

if we using scope varible

let a=30;

function esma_example(){

    let a = 40;

    console.log("value of a under function :"+a);

}

esma_example()

console.log("value of a:"+a);

output-

value of a under function :40

value of a:30

Nodejs- module exports

module exports

->it will help to get/fetch one module data into another module

main.js 

var name = "Kamal"

var person = function(a,b){

    var c = a+b

    console.log("sum of "+ a +" and "+ b +" is "+ c)

}

person(5,5);

module.exports.exp_example = name;

global_object.js

var main = require("./main")

console.log(__dirname)

console.log(__filename)

console.log(main.exp_example)

OUTPUT-

K:\NodeJs\Node Basics\chapter-1

K:\NodeJs\Node Basics\chapter-1\globalObject.js

Kamal

Nodejs - Global Objects

 Global Objects

-> We have two js files for accessing main.js objects we are using this functions in object.js

1)main.js

var person = function(a,b){

    var c = a+b

    console.log("sum of "+ a +" and "+ b +" is "+ c)

}

person(5,5);

2)global_objects.js

var main = require("./mian")

console.log(__dirname)

console.log(__filename)

output

sum of 5 and 5 is 10 K:\NodeJs\Node Basics\chapter-1 K:\NodeJs\Node Basics\chapter-1\globalObject.js

Nodejs - Arrow Functions

Arrorw Functions :

    

        -> Its a shortest way to define functions.

             EXAMPLE:    

            

            Without Parameter

                    var kamal =()=>{console.log("Its a arrow functions")}

                   

                     kamal()            ///call function

            With Parameter

                    var kamal =(a)=>{console.log("value of a is :"+a)}

                    

                    kamal(5)          ///call function

            With Multiple Parameter

                    var kamal =(a,b)=>{

                                

                    var  c=a+b

                    console.log("value of c is :"+c)}

                    

                    kamal(5,5)          ///call function

OUTPUT- value of c is :10

Nodejs - Anonymous Functions

 Anonymous Functions

    -> define variable then function

    Ex.-        !) Without parameter.... 

                     ver kamal = function(){

                        console.log("Its a anontmous function");

                    }

                    kamal()              ///call functions

                !!) With parameter...

                    var kamal = funtion(a,b){

                     var c = a+b

                    console.log("The value of  c is : "+c)

                     }

                    kamal(5,5)          //call functions

OUTPUT -  The value of  c is :10

NOTE: There is no name infront of function thats why its a anonymous function.

NodeJs - Node Http & Query String

Basic Conecpts For Creating server and response code

Its a inbuilt modul with help of this module we can perform meny operationsIt Handle - Request & Response beacause it is a Hypertext Text Transfer Protocol(get request from user and give response to server)

1) For creating server we need Http module..

2) Url Handling : For Handlng Url we can use

var http = require('http');  --> inbuild module it access via direct requre method can access

var server = http.createServer(function(req , res){       ///create server

//Request Status , Content Type

server.writeHead(200,{"content-type":"text/plain"})

var url = req.url;                 //Url Handling

res.write(url)

res.end('Response End')     //print message

}) .listen(3000);

Note : Query String = Send Variable in browser with url

Url Handling

var http = require('http');  --> inbuild module it access via dirct method

var url = require('url');             //Handling Querystring

var server = http.createServer(function(req , res){       ///create server

server.writeHead(200,{"content-type":"text/plain"})

var result = url.parse(www.google.com?id=10, true).query;

res.write(res.name);   //things whinch want to get like name

}) .listen(3000);

Run-> localhost://300

Kotlin - Functions

 function with two Int parameters and Int return type.

fun sum(a: Int, b: Int): Int {

    return a + b

}

sum of 3 and 5 is 8

Open in Playground →

Target platform: JVMRunning on kotlin v.1.6.0

A function body can be an expression. Its return type is inferred.

fun sum(a: Int, b: Int) = a + b

sum of 19 and 23 is 42