Node JS Basic

Node JS Basic

Functional expression

function greet(){
     console.log("hello welcome");
}
greet();

var anynomousfunction =  function (){
 console.log("hello This is anynomous function ");
}
anynomousfunction ();

-------------
pass function as param

function doGreet(func) {
  func();
}

doGreet( anynomousfunction  );

-----------------

Module and require 

data.js

var counter= function(arr) {
 return 'There are' + arr.length . ' element ';
}
var adder = function(){
   return ` the sum is $(a+b) `;
}

var PI = 3.1416;

////// module.exports = counter; ///one
module.exports.counter = counter;
module.exports.added = added;
module.exports.PI= PI;


or  we can do this
module.exports = {
  counter : counter,
  PI:PI,
  adder: adder
}

app.js

var data= require('./data');  // is  {module.exports}
console.log(data.counter(['a','b','c'] ));
console.log(data.adder(5, 6 ));

----------------------

Event emitter

var events = require("events");
var myEmitter = new  events.EventEmitter();

myEmitter.on( 'someEvent' , function(msg){
 console.log(msg);
});

myEmitter.emit( 'someEvent' , function(msg) {

});

------------------

var events = require("events");
var util = require("util");


var Person = function (name) {
 this.name = name;
}

util.inherits(Person, events.EventEmitter );

var james = new Person("james");
var mary = new Person("mary");

var people = [james, mary];


people.forEach( function( person){
 person.on ( 'speak', function(msg){
   console.log(person.name + "said" + msg);
  });
});

james.emit("speak", "hey dudes");
mary.emit("speak", "cool");

-------------------

Reading and writing files

//file system module for node js

var fs = require("fs);

// read file synchronous

var readMe = fs.readFileSync( "readme.txt", "utf8");

console.log(readMe);

// read/write file normal 

fs.readFile( "readme.txt", "utf8", function(err, data){

fs.writeFile("newFile.txt", readMe); 

});

// write file synchronous
fs.writeFileSync("newFile.txt", readMe); //filename , data to write

----------------------

Create and remove directory

var fs = require("fs);

//remove file
fs.unlink("filename");

//synchronous
fs.mkdirSync("dirname");
fs.rmdirSync("dirname");


//asynchronous
fs.mkdir("dirname", function (){

});
fs.rmdir("dirname", function (){

});
// to remove dir dir should be empty
//delete file using unlink

------------------------

Client and server

var http = require("http");

var server = http.createServer(function( req, res ){
 console.log("request is made"+ req.url);
   res.writeHead(200, {"Content-Type": "text/plain" });
   res.end(" hey ninjas");

});

server.listen(3000, "127.0.0.1" );
console.log(" now listenung to port 3000");
---------------

Header
conteny-Type
Status

-------------------------

Stream and buffer

//reading streams
//chunk > buffer > stream

var http = require("http");

var fs = require("fs");

var myReadStream = fs.createReadStream(__dirname + "/readMe.txt", "utf8" );

var myWriteStream = fs.createWriteStream(__dirname + "/writeMe.txt", "utf8" );

myReadStream.on("data", function( chunk) {
  console.log("new chunk received");
console.log(chunk);
myWriteStream.write(chunk);
});

PIPES

myReadStream.pipe(myWriteStream);

// pipe to res in for server

myReadStream.pipe(res);

Serving HTML page

var server = http.createServer(function( req, res ){
 console.log("request is made"+ req.url);
   res.writeHead(200, {"Content-Type": "text/html" });

var myReadStream = fs.createReadStream(__dirname + "/index.html", "utf8" );

myReadStream.pipe(res); 

});

Serving JSON

var server = http.createServer(function( req, res ){
 console.log("request is made"+ req.url);
   res.writeHead(200, {"Content-Type": "text/json" });
   var myObj = {
   name: 'Niral',
   job : 'developer',
   }

  res.end(JSON.stringify(myObj));

});

Basic Routing

var server = http.createServer(function( req, res ){
 console.log("request is made"+ req.url);

if(res.url === "/home" || res.url === "/") {
    res.writeHead(200, {"Content-Type": "text/html" });
     fs.createReadStream(__dirname + "/index.html" ).pipe(res);
}else if(res.url === "/contact") {
     res.writeHead(200, {"Content-Type": "text/html" });
     fs.createReadStream(__dirname + "/contact.html" ).pipe(res);
} else if(res.url === "/api/ninjas") {

     res.writeHead(200, {"Content-Type": "application/json" });
          var myObj = {
         name: 'Niral',
         job : 'developer',
    }

      res.end(JSON.stringify(myObj));

}
});

---------------------------
Thanks to
The net ninja
https://www.youtube.com/playlist?list=PL4cUxeGkcC9gcy9lrvMJ75z9maRw4byYp

Author : Niral

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