Okay here is the general goal of this code. I am using TinyPNG's API to condense a folder of png files. I have an input folder with a number of files named filename.png. This code reads the directory of file names into an array files, then creates read and write streams for those files to be sent to the API, processed, and then returned so it can be written to a file in the output folder. I know the code works for one file, but any more than that throws an exception of write after end because the pipe is automatically closed after the first one. I have tried setting up the input and output as arrays and that just throws another exception.
Any hints on how to set up multiple read and write streams would be awesome and very useful to everyone :).
Current code:
var fs = require('fs');
var inputFolder = "input/";
var outputFolder = "output/";
var https = require("https");
var key = "GETYOUROWNFREEONEFROMTINYPNG.ORG";
process.env.NODE_TLS_REJECT_UNAUTHORIZED = "0";
var options = require("url").parse("https://api.tinypng.com/shrink");
options.auth = "api:" + key;
options.method = "POST";
console.log("Reading files...");
fs.readdir("./input", function (err, files) {
if (err) throw err;
console.log(files.length + " files read...");
var input;
var output;
var request;
for(var i = 0; i < files.length; i++)
{
input = fs.createReadStream(inputFolder + files[i]);
output = fs.createWriteStream(outputFolder + files[i]);
request = new https.request(options, function(response) {
if (response.statusCode === 201) {
/* Compression was successful, retrieve output from Location header. */
https.get(response.headers.location, function(response) {
response.pipe(output);
});
} else {
/* Something went wrong! You can parse the JSON body for details. */
console.log("Compression failed");
}
});
input.pipe(request);
}
});
Here is the fixed file for others to use thanks to the answer provided by #Wyatt:
var fs = require('fs');
var inputFolder = "input/";
var outputFolder = "output/";
var https = require("https");
var key = "WotZ46HnxPl_HwpT3uZjtY_0f8fMEiSR";
process.env.NODE_TLS_REJECT_UNAUTHORIZED = "0";
var options = require("url").parse("https://api.tinypng.com/shrink");
options.auth = "api:" + key;
options.method = "POST";
console.log("Reading files...");
fs.readdir("./input", function (err, files) {
if (err) throw err;
console.log(files.length + " files read...");
var input, request;
for(var i = 0; i < files.length; i++){
input = fs.createReadStream(inputFolder + files[i]);
request = closureRequest(fs.createWriteStream(outputFolder + files[i]));
input.pipe(request);
}
});
function closureRequest(output){
return new https.request(options, function(response) {
if (response.statusCode === 201) {
/* Compression was successful, retrieve output from Location header. */
https.get(response.headers.location, function(response) {
response.pipe(output);
});
} else {
/* Something went wrong! You can parse the JSON body for details. */
console.log("Compression failed");
}
});
}
You are repeatedly reassigning the output variable in your loop, while the request callback is trying to refer to it. You can capture each value in a closure to get around this.
...
function closureRequest(output){
return new https.request(options, function(response) {
if (response.statusCode === 201) {
/* Compression was successful, retrieve output from Location header. */
https.get(response.headers.location, function(response) {
response.pipe(output);
});
} else {
/* Something went wrong! You can parse the JSON body for details. */
console.log("Compression failed");
}
});
}
var input
, request
;
for(var i = 0; i < files.length; i++){
input = fs.createReadStream(inputFolder + files[i]);
request = closureRequest(fs.createWriteStream(outputFolder + files[i]));
input.pipe(request);
}
Related
first of all, pardon me if this is not the correct way of asking a question but this is my first post.
I am working on a university project and am new to JavaScript (and subsequently, jQuery and NodeJS). I am trying to make a system that will take a CSV file, process it and load the results into a database ready to be used by the rest of the system.
I have made it so that I can upload the file to a directory and have a function to process the CSV file into a JSON object (we have only just started to cover databases so I will have to modify this to store in the database), but the problem I'm currently facing is this...
How do I pass/read the uploaded file into the function for processing?
I have searched around and have found similar questions, but these are either usually using PHP or cover different aspects of my issue, without actually touching upon my problem.
I'm sorry if this is something very basic that I am missing, but I'm pulling my hair out over this and can't progress to the rest of the tasks until i have the first part in place - upload, process and store the CSV file.
I will take any advice, either directly related to the issue or pointers from experience that you think I may face, and thank you for you time.
Upload
var express = require("express");
var multer = require("multer");
var fs = require("fs");
var path = require("path");
var app = express();
var upload = multer({ dest: './uploads/'});
app.use(express.static('public'));
app.use(upload);
app.post('/api/csvUpload',function(req,res) {
upload(req,res,function(err) {
// console.log(req.body);
// console.log(req.files);
if(err) {
return res.end("Error uploading file");
}
else{
res.send("File is uploaded");
}
});
});
var server = app.listen(8081, function () {
var host = server.address().address;
var port = server.address().port;
console.log("working on port 8081!");
});
<!DOCTYPE html>
<html>
<head>
<title>Home Page</title>
</head>
<body>
<form id="uploadForm" action="/api/csvUpload" method="post" enctype="multipart/form-data">
<input type="file" name="csvFile">
<input type="submit" value="Upload File" />
</form>
</body>
</html>
CSV to JSON
//This will process and convert a CSV file in to a JSON objec
function csvJson(csv) {
var lines = csv.split("\n");
var result = [];
var headers = lines[0].split(",");
for(var i = 1; i < lines.length; i++) {
var obj = {};
var currentLine = lines[i].split(",");
for(var j = 0; j < headers.length; j++) {
obj[headers[j]] = currentLine[j];
}
result.push(obj);
}
return JSON.stringify(result);
};
//Below is for testing purposes
var testCSV = "userName, firstName, lastName, studentID, course\n" +
"username1,first1,last1,123456,Software Engineering\n" +
"username2,first2,last2,234567,Software Engineering\n" +
"username3,first3,last3,345678,Software Engineering\n" +
"username4,first4,last4,456789,Software Engineering";
var processedCSV = csvJson(testCSV);
console.log(processedCSV);
Because it's not completely clear for me how the files are uploaded, I'll start with the functions that gives the ability to load a (CSV)-file.
For loading a file or url you can use XMLHttpRequest, more on this can be found at W3Schools. This is a really powerful object, and I would really advice to read more into this.
/**
* Loads file using XMLHttpRequest
* #param {String} path
* #param {Function} success
* #param {Function} error
*/
function loadFile(path, success, error) {
var xhr = new XMLHttpRequest();
xhr.onreadystatechange = function () {
if (xhr.readyState === XMLHttpRequest.DONE) {
if (xhr.status === 200) {
if (success)
success(csvToJSON(xhr.responseText));
} else {
if (error)
error(xhr);
}
}
};
xhr.open("GET", path, true);
xhr.send();
}
To use this function, simply execute the following code:
loadFile('Link_to_CSV_file.csv', function (data) {
myFunction(data);
}, function (xhr) {
console.error(xhr);
});
As soon the data is succesfully loaded, myFunction() will be executed with the data from loadFile(). This can be used in the function.
Finally, load the CSV-data in a function:
function myFunction(data){
console.log(data);
}
PS: I would advice to convert the CSV file to JSON if you want to handle it in a javascript-function, if you're using Node.js, check out How to convert CSV to JSON in Node.js.
I am working on a Team Treehouse project that builds a dynamic website with Node.js. The user enters in a username into the search field and it displays the user's avatar, number of badges earned and the number of JavaScript points. For some reason when I enter in the user name and click search the page just goes blank. I think there might be something wrong with the 303 redirection in my router.js file. I'm still fairly new to coding so any insight would be very helpful. Here are each of my js files.
/*****app.js file******/
var router = require('./router.js');
//Problem: We need a simple way to look at a user's badge count and JavaScript points from a web browser
//Solution: Use Node.js to perform the profile look ups and serve our templates via HTTP
//Create a web server
var http = require('http');
http.createServer(function (request, response) {
router.home(request, response);
router.user(request, response);
}).listen(3000);
console.log('Server running at http://<workspace-url>');
/*****router.js file******/
var Profile = require("./profile.js");
var renderer = require('./renderer');
var querystring = require('querystring');
var commonHeader = {'Content-Type': 'text/html'};
// Handle the HTTP route GET / and POST / i.e. Home
function home(request, response) {
//if url == "/" && GET
if (request.url === '/'){
if (request.method.toLowerCase() === "get") {
//show search
console.log(request.url);
response.writeHead(200, commonHeader);
renderer.view('header', {}, response);
renderer.view('search', {}, response);
renderer.view('footer', {}, response);
response.end();
}
else {
//if url == "/" && POST
//get the post data from body
request.on('data', function(postBody){
//extract the username
var query = querystring.parse(postBody.toString());
//redirect to /:username
response.writeHead(303, {'Location': '/' + query.username });
response.end();
});
}
}
}
// Handle the HTTP route for GET /:username i.e. /chalkers
function user(request, response) {
//if url == "/...."
var username = request.url.replace('/', '');
if(user.name.length > 0){
response.writeHead(200, commonHeader);
renderer.view('header', {}, response);
//get json from Treehouse
var studentProfile = new Profile(username);
//on "end"
studentProfile.on("end", function(profileJSON){
//show profile
//Store the values which we need
var values = {
avatarUrl: profileJSON.gravatar_url,
username: profileJSON.profile_name,
badges: profileJSON.badges.length,
javascriptPoints: profileJSON.points.JavaScript
}
//Simple response
renderer.view('profile', values, response);
renderer.view('footer', {}, response);
response.end();
});
//on "error"
studentProfile.on("error", function(error){
//show error
renderer.view('error', {errorMessage: error.message}, response);
renderer.view('search', {}, response);
renderer.view('footer', {}, response);
response.end();
});
}
}
module.exports.home = home;
module.exports.user = user;
/*****profile.js file*******/
var EventEmitter = require("events").EventEmitter;
var http = require("http");
var util = require("util");
/**
* An EventEmitter to get a Treehouse students profile.
* #param username
* #constructor
*/
function Profile(username) {
EventEmitter.call(this);
profileEmitter = this;
//Connect to the API URL (http://teamtreehouse.com/username.json)
var request = http.get("http://teamtreehouse.com/" + username + ".json", function(response) {
var body = "";
if (response.statusCode !== 200) {
request.abort();
//Status Code Error
profileEmitter.emit("error", new Error("There was an error getting the profile for " + username + ". (" + http.STATUS_CODES[response.statusCode] + ")"));
}
//Read the data
response.on('data', function (chunk) {
body += chunk;
profileEmitter.emit("data", chunk);
});
response.on('end', function () {
if(response.statusCode === 200) {
try {
//Parse the data
var profile = JSON.parse(body);
profileEmitter.emit("end", profile);
} catch (error) {
profileEmitter.emit("error", error);
}
}
}).on("error", function(error){
profileEmitter.emit("error", error);
});
});
}
util.inherits( Profile, EventEmitter );
module.exports = Profile;
/*****renderer.js file*******/
var fs = require('fs');
function mergeValues(values, content) {
//Cycle over the keys
for(var key in values) {
//Replace all the {{key}} with the value from the values object
content = content.replace('{{' + key + '}}', values[key]);
}
//return merged content
return content;
}
function view(templateName, values, response) {
//Read from the template file
var fileContents = fs.readFileSync('./views/' + templateName + '.html', {encoding: 'utf8'});
//Insert values in to the content
fileContents = mergeValues(values, fileContents);
//Write out the contents to the response
response.write(fileContents);
}
module.exports.view = view;
Treehouse changed from http to https and so this example code doesn't work any longer. The reason for that is in the profile.js file. You are making calls for an http site and it doesn't exist. You need to change the code (only in profile.js) to make it connect to the https site instead.
var http = require("http");
should be changed to
var https = require("https");
and with that all references to the variable in your profile.js code should be changed to https.
As well as the hard-coded URL start:
var request = http.get("http://teamtreehous...
should be
var request = https.get("https://teamtreehous...
That should resolve the problem. Good luck!
In order to get your code in the profile.js file to run, you need to change some instances of the "http" module to "https" but, and this is important, not all instances.
What needs to remain http is the the status code error on the profile.js page. This line of code is correct:
profileEmitter.emit("error", new Error("There was an error getting the profile for " + username + ". (" + http.STATUS_CODES[response.statusCode] + ")"));
But all other instances of the http module need to change to https. For example, these lines are correct:
var url = "https://teamtreehouse.com/" + username + ".json";
var request = https.get(url, function(response){
Remember to require both modules at the top of profile.js page
var http = require("http");
var https = require("https");
I am developing an extension for Mozilla Firefox, where I override the native listener with my own and monitor all HTTP requests, as shown in the post here:
http://www.softwareishard.com/blog/firebug/nsitraceablechannel-intercept-http-traffic/
I monitor those requests that reside under a specific domain and change their corresponding response body, with the response body I receive from my own XMLHTTPRequest. For text files, everything is working fine.
However, I face a problem while downloading images. For some reason, when I write the incoming data to the stream and then, try to open the image, I get the error that the image contains errors and cannot be displayed.
What am I possibly doing wrong?
Update: I provide some code, in order to clarify my approach.
var xmlRequest = Cc['#mozilla.org/xmlextras/xmlhttprequest;1'].createInstance(Ci.nsIXMLHttpRequest);
...
xmlRequest.open('GET', xmlRequestURL, false);
xmlRequest.send(null);
function TracingListener() {}
TracingListener.prototype = {
originalListener: null,
onStartRequest: function (request, context) {
httpChannel = request.QueryInterface(Ci.nsIHttpChannel);
requestURL = httpChannel.URI.spec;
try {
this.originalListener.onStartRequest(request, context);
}
catch (ex) {
request.cancel(ex);
}
},
onDataAvailable: function (request, context, inputStream, offset, count) {
httpChannel = request.QueryInterface(Ci.nsIHttpChannel);
requestURL = httpChannel.URI.spec;
//Read the contents from the stream, but ignore them.
var binaryInputStream = CCIN('#mozilla.org/binaryinputstream;1', 'nsIBinaryInputStream');
binaryInputStream.setInputStream(inputStream);
var binaryOutputStream = CCIN('#mozilla.org/binaryoutputstream;1', 'nsIBinaryOutputStream');
var data = binaryInputStream.readBytes(count);
//Delay the call to the original listener.
},
onStopRequest: function (request, context, statusCode) {
httpChannel = request.QueryInterface(Ci.nsIHttpChannel);
requestURL = httpChannel.URI.spec;
//Check if the response is successful.
if(xmlRequest.status == 200) {
try {
var responseLen = xmlRequest.getResponseHeader("Content-Length");
var response = xmlRequest.response;
var storageStream = CCIN('#mozilla.org/storagestream;1', 'nsIStorageStream');
storageStream.init(8192, responseLen, null);
var binaryOutputStream = CCIN('#mozilla.org/binaryoutputstream;1', 'nsIBinaryOutputStream');
binaryOutputStream.setOutputStream(storageStream.getOutputStream(0));
binaryOutputStream.writeBytes(response, responseLen);
//Make the call to the original listener.
this.originalListener.onDataAvailable(request, context, storageStream.newInputStream(0), 0, responseLen);
}
catch (e) {
dumpError(e);
}
//Pass it to the original listener
this.originalListener.onStopRequest(request, context, statusCode);
}
else {
console.log('[INFO] onStopRequest not processed, status is ' + xmlRequest.status + ', for URL: ' + requestURL);
}
}
}
var observer = {
httpRequestObserver: {
observe: function (request, aTopic, aData) {
httpChannel = request.QueryInterface(Ci.nsIHttpChannel);
requestURL = httpChannel.URI.spec;
if(mustBeMonitored(requestURL)) {
console.log('[INFO] Observing URL: ' + requestURL);
if (aTopic == 'http-on-modify-request') {
console.log('[INFO] ' + aTopic + ' for URL: ' + requestURL);
var newListener = new TracingListener();
request.QueryInterface(Ci.nsITraceableChannel);
newListener.originalListener = request.setNewListener(newListener);
}
}
},
register: function () {
observerService.addObserver(observer.httpRequestObserver, 'http-on-modify-request', false);
},
unregister: function () {
observerService.removeObserver(observer.httpRequestObserver, 'http-on-modify-request');
},
QueryInterface: function (aIID) {
/*if (typeof Cc == "undefined") {
var Cc = components.classes;
}
if (typeof Ci == "undefined") {
var Ci = components.interfaces;
}*/
if (aIID.equals(Ci.nsIObserver) || aIID.equals(Ci.nsISupports))
return this;
throw components.results.NS_NOINTERFACE;
}
}
};
Finally, I was able to detect the problem. For the XMLHttpRequest, I had to specify its response type as follows:
xmlRequest.responseType = 'arraybuffer';
Then, the response was stored in a JavaScript ArrayBuffer, which I had to transform into a Uint8Array and then, store it into the stream.
This solution applies for both binary and text files.
I have a file called node.js:
var net = require('net');
var crypto = require('crypto');
//sjcl
var sjcl = require('./sjcl');
//retrive fb profile
var loadFb = require('./loadFb.js');
var loadFeed = require('./loadFeed.js');
//read json user file
var fs = require('fs');
var text = fs.readFileSync(__dirname + '/users','utf8');
var HOST = 'localhost';
var PORT = 7000;
net.createServer(function(sock) {
// We have a connection - a socket object
console.log('CONNECTED: ' + sock.remoteAddress +':'+ sock.remotePort);
// Add a 'data' event handler to this instance of socket
sock.on('data', function(data) {
console.log('User request profile of: ' + data);
//var date = (data.toString()).split("***");
//var from = date[1];
loadFb(extendetPath, function(pageData)
{
loadFeed(extendetPath2, function(pageData2)
{
var fs = require('fs');
var profileText = fs.readFileSync('/tmp/profile','utf8');
console.log(profileText);
sock.write(profileText);
});
});
});
// Add a 'close' event handler to this instance of socket
sock.on('close', function(data) {
console.log('CLOSED: ' + sock.remoteAddress +' '+ sock.remotePort);
});
}).listen(PORT);
console.log('Server listening on ' + HOST +':'+ PORT);
function returnKeyFromUser(id)
{
//text
var trovata = false;
var dati = JSON.parse(text);
for(var i=0; i<dati.friendlist.friend.length && trovata==false; i++)
{
var user = (dati.friendlist.friend[i].username).replace("\n","");
var userID = (id).replace("\n","");
if(user==userID)
{
trovata=true;
return ((dati.friendlist.friend[i].publicKey).toString()).replace("\n","");
}
}
if(trovata==false)
return null;
}
There is a small http server that receives a facebook username and what he have to do is retrieve 2 page:
a graphapi with the profile information, and a graphapi with the feed informations of a facebook profile
I copy the other two files:
var https = require('https');
module.exports = function(path, callback) {
var options = {
host: 'graph.facebook.com',
port: 443,
path: (path.toString()).replace("\n",""),
method: 'GET'
};
var req = https.get(options, function(res) {
var pageData = "";
if((path.toString()).indexOf("/")==0 && (path.toString()).indexOf("/GET /`HTTP/")!=0)
//for load only (I hope facebook profile)
{
console.log(options);
res.setEncoding('utf8');
res.on('data', function (chunk) {
pageData += chunk;
});
res.on('end', function()
{
var fs = require('fs');
fs.writeFile("/tmp/profile", pageData, function(err) {
if(err) {
console.log(err);
} else {
console.log("The file was saved!");
}
});
//callback(pageData);
return;
});
}
});
};
3° file
var https = require('https');
module.exports = function(path, callback) {
var options = {
host: 'graph.facebook.com',
port: 443,
path: (path.toString()).replace("\n",""),
method: 'GET'
};
var req = https.get(options, function(res) {
var pageData = "";
if((path.toString()).indexOf("/")==0 && (path.toString()).indexOf("/GET / HTTP/")!=0) //for load only (I hope facebook profile)
{
console.log(options);
res.setEncoding('utf8');
res.on('data', function (chunk) {
pageData += chunk;
});
res.on('end', function()
{
var fs = require('fs');
fs.appendFile('/tmp/profile', "***"+pageData, function (err) {
if (err) throw err;
console.log('It\'s saved!');
});
callback(pageData);
});
}
});
};
I don't know If there is a way to call the two file in the first file node.js but what I done is this: (to call from node.js the fist file, and from the second file call the third)
in node.js file I call the first file loadFb.js with this command:
loadFb(extendetPath, function(pageData)
{
This call saves a file on my tmp profile directory and inside I call the other file loadFeed that appends some text.
After that I have to send the entire information to the client but I have a mistake.
In order the nodejs correctly call loadFb and he write tmp - profile, than he call loadFeed
but before appending the information the node call back to the client only the half of informations that I need.
I'm not a good nodejs programmer, this is a work for my thesis.
Can someone help me?
Let's look at the following code:
res.on('end', function()
{
var fs = require('fs');
fs.appendFile('/tmp/profile', "***"+pageData, function (err) {
if (err) throw err;
console.log('It\'s saved!');
});
callback(pageData);
});
What it does it runs the asynchronous method appendFile and immediately after that calls callback. So when the code in the callback is executed, the file is not updated yet. You need to move the callback(pageData); to the appendFile's callback. And you need to review you code keeping this in mind because I see that the same fix should be made in another file so maybe there are some similar places as well.
I have written a http server using node js
var sys = require("sys"),
http = require("http"),
url = require("url"),
path = require("path"),
fs = require("fs");
http.createServer(function(request, res) {
var parsed_url = url.parse(request.url);
var uri = parsed_url.pathname;
if(uri === "/test"){
res.writeHead(200, {'Content-Type': 'text/javascript'});
request.addListener('data', function (chunk) {
var data = eval("(" + chunk + ")");
console.log(data[0].id);
})
request.addListener('end', function() {
console.log('end triggered');
res.write("Post data");
res.end();
});
}
}).listen(8080);
and i am trying to send back response of ajax request but i am unable to receive any response. Here is the code for ajax request ,
var myhttp = new XMLHttpRequest();
var url = "http://localhost:8080/test";
var data = [{"a":"1"},{"b":"2"},{"c":"3"}];
var dataJson = JSON.stringify(data);
myhttp.open('POST', url, true);
myhttp.send(dataJson);
myhttp.onreadystatechange = function() {
if ((myhttp.readyState == 4) && (myhttp.status == 200)){
alert(myhttp.responseText);
}
else if ((myhttp.readyState == 4) && (myhttp.status != 200))
{
console.log("Error in Connection");
}
Can anyone help me what i am doing wrong ...
Thanks
Vinay
Your code is almost right but on your code sample you have
console.log(data[0].id)
the data object has no property id so if you only have
console.log(data[0])
there you have a response like
{ a: '1' }
therefore you can access the property a by doing
console.log(data[0].a);
UPDATED Updated with a full example
One more thing is that you are using eval and node comes with JSON.parse bundle with it so the snippet below is how i made it work
File: app.js
var sys = require("sys"),
http = require("http"),
url = require("url"),
path = require("path"),
fs = require("fs");
http.createServer(function(request, res) {
var parsed_url = url.parse(request.url);
var uri = parsed_url.pathname;
if(uri === "/test"){
res.writeHead(200, {'Content-Type': 'text/javascript'});
request.addListener('data', function (chunk) {
// removed this - eval("(" + chunk + ")");
var data = JSON.parse(chunk);
console.log(data[0].a);
})
request.addListener('end', function() {
console.log('end triggered');
res.write("Post data");
res.end();
});
} else if(uri === "/") {
fs.readFile("./index.html",function(err, data){
if(err) throw err;
res.writeHead(200, {'Content-Type': 'text/html'});
res.end(data);
});
}
}).listen(8080);
On the same directory create a file index.html with the following:
<html>
<head>
<script type="text/javascript" charset="utf-8">
var myhttp = new XMLHttpRequest();
var url = "http://localhost:8080/test";
var data = [{"a":"1"},{"b":"2"},{"c":"3"}];
var dataJson = JSON.stringify(data);
myhttp.open('POST', url, true);
myhttp.send(dataJson);
myhttp.onreadystatechange = function() {
if ((myhttp.readyState == 4) && (myhttp.status == 200)){
alert(myhttp.responseText);
}
else if ((myhttp.readyState == 4) && (myhttp.status != 200))
{
console.log("Error in Connection");
}
}
</script>
</head>
<body>
</body>
</html>
That is a complete working example of what you want.
With regards to the same origin policy issues you were having is mainly due to the fact that you cant POST data between 2 different domains via ajax unless you use some tricks with iframes but that is another story.
Also i think is good for anyone to understand the backbone of a technology before moving into frameworks so fair play to you.
good luck
You have to read the data in a different way. Posted data arrives on a node server in chunks (the 'data' event), that have to be collected until the 'end' event fires. Inside this event, you are able to access your payload.
var body = '';
request.addListener('data', function (chunk) {
body += chunk;
});
request.addListener('end', function() {
console.log(body);
res.write('post data: ' + body);
});
Additionaly, there seem to be some issues with your client-side code (especially concerning the status-code checks), but i can't really help you with those as i always work with frameworks like jQuery to manage async requests.
If you want to build reliable node.js servers for web use, i highly recommend the high-performance HTTP-Framework Express. It takes away alot of the pain when developing a web-based server application in node and is maintained actively.