nodejs_training/coremodules.js

Demo of nodejs

//core modules are modules provided by node js for devloping basic apps in node.js.
var fs = require('fs');//filesystem used to read and write to file

var os = require('os');

var http = require('http');

var emitter = require('events');

/*
//use readFileSync to read contents of the file
function readMyFile() {
    var fileName = 'firstExample.js';
    var contents = fs.readFileSync(fileName, 'utf8');
    console.log(contents);
}

function readAsyncFile() {
    fs.readFile('firstExample.js', 'utf8', function(err, res){
       if(err) {
           console.log(err.message);
           return;
       } 
        console.log(res);
    });
}

//readMyFile();
//readAsyncFile();
//console.log("Doing some other job");

//fs.appendFile('sampleExample.txt', 'Contents to be appended', (err) => console.log(err));

fs.open('SampleExample.txt', 'a+', function(err, fd){
    var buffer = new Buffer("Some content to add");
    fs.write(fd,buffer, 0, buffer.length, null, function(err, written, buffer){
        console.log("written content:" + written);
        fs.close(fd, () => console.log("Operation complete"));
    })
})

fs.stat('SampleExample.txt', (err, stats) =>{
    console.log(stats);
    console.log("is it a file?" + stats.isFile());
    console.log("Is is a directrory?" + stats.isDirectory());
});

//OS Module
console.log("architecture:" + os.arch());
console.log("the os:" + os.platform());
console.log("CPUS:" );
console.log(os.cpus());
console.log("Free memory:" + os.freemem());
console.log("Home dir:" + os.homedir());
console.log("Hostname:" + os.hostname());


///Timer

setInterval(() => console.log(Date()), 1000);

//there is another function called setTimeout which is to invoke a function after the specified amount of time is completed
setTimeout(() => {console.log("Nodejs time function")}, 1000);

*/
//HTTP
/*
function postErrorPage(res) {
    res.writeHead(404, {'Content-type': 'text/html'});
    res.write("Opps! something bad happened");
    res.end();
}

http.createServer(function(req,res){
    console.log("request has come");
    //res.write("Page is processed and sent as response");
    //    res.end();
    
    if(req.method =='GET' && req.url == '/') {
        res.writeHead(200, {'Content-type': 'text/html'});
        fs.createReadStream('./HomePage.html').pipe(res);
       }
    else {
        postErrorPage(res);
    }
}).listen(1234);
*/

//Event emitter
/*
var log = new emitter.EventEmitter();

function onClick() {
    for(var i =0; i< 100; i++) {
        console.log("click event fired at receiver" + i);
    }
}

//register the click event to event loop
log.on('click', function(callBackFunc){
    callBackFunc();
})

log.emit('click', onClick); //this will trigger click event

 for(var i =0; i< 100; i++) {
        console.log("source" + i);
    }
*/
var emitter1 = require('./eventEmitterDemo').logger;

function onError() {
    var msg = "Err occured at " + Date();
    fs.appendFile("Errors.txt", msg, (err) => console.log(err));
}

console.log("Doing some big job");
console.log("Some error happened");
emitter1.emit("error", onError);