01.Hello Node.js

var http=require('http');
var fs=require('fs');
var path=require('path');
var mime=require('mime');
var cache={};

function send404(response){
    response.writeHead(404,{'Content-Type':'text/plain'});
    response.write('Error 404:resource you requested not found.');
    response.end();
}

function sendFile(response,filePath,fileContents){
    response.writeHead(200,{'Content-Type':mime.lookup(path.basename(filePath))});
    response.end(fileContents);
}

function serveStatic(response,cache,absPath){
    if(cache[absPath]){
        sendFile(response,absPath,cache[absPath]);
    }else{
        fs.exists(absPath,function(exists){
            if(exists){
                fs.readFile(absPath,function(err,data){
                    if(err){
                        send404(response);
                    }else{
                        cache[absPath]=data;
                        sendFile(response,absPath,data)
                    }
                }
                );
                
            }else{
                send404(response);
            }
        }
        );
    }
}

var server=http.createServer(function(request,response){
    var filePath=false;
    
    if(request.url=="/"){
        filePath='public/index.html';
    }else{
        filePath='public'+request.url;
    }
    
    var absPath='./'+filePath;
    serveStatic(response,cache,absPath);
}
);

server.listen(3000,function(){
    console.log('Server is listenning on port 3000.');
});