Program samples added till FileServer concepts in Node.js

Author: gevic

README.md

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 # Node.js-tutorials
 Node.js small code tutorials for Beginners. 
+
+## What is Node.js
+It is a an open source server enviroment which user JavaScript on the server. It uses asynchronous programming.
+
+## Why Node.js
+Let's deal with it using an example. A common task on web server is to open a file on the server and return to the client.
+
+Here is how PHP and ASP will handle it:
+* Sends the task to the computer's file system.
+* Waits while the file system opens and reads the file.
+* Returns the content to the client.
+* Ready to handle the next request.
+
+Here is how Node.js handles a file request:
+* Sends the task to the computer's file system.
+* Ready to handle the next request.
+* When the file system has opened and read the file, the server returns the content to the client.
+
+It eliminate the wait time here. Hence, is memory efficient.
+
+## What can it do?
+* It can generate dynamic page content
+* It can create, open, read, write, delete, and close files on the server
+* It can collect form data
+* It can add, delete, modify data in your database
+
+This intro part is taken from https://www.w3schools.com/nodejs/nodejs_intro.asp.
+
+

createModules.js

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+// Apart from built-in modules, you can define you own modules
+// Let's say our module returns date
+// {exports} keywors is used to make the function available outside the module file 
+exports.getDateTime = function() {
+  return Date();
+}

fileServer.js

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+// Node.js as File server
+// file system module in node.js allow you to work with the file system on our computer.
+var fileSystem = require('fs'); // can create, read, update delete, rename file
+var http = require('http');
+
+// To read files i.e. fileSystem.readFile(). Say you have html file name operationTest.html
+http.createServer(function (req, res){
+  fileSystem.readFile('operationTest.html', function (err, data){ // reads the entire content of the file asynchronously
+    res.writeHead(200, {'Content-Type':'text/html'});
+    res.write(data);
+    res.end();  
+  });
+}).listen(8080)
+
+// basicly you can run your html files using this
+
+// Create files using appendFile (created if not present)
+fileSystem.appendFile('createFile.txt', 'Yupee created!', function(err){
+  if(err) throw err;
+  console.log('Saved!');
+});
+
+// open method
+fileSystem.open('createFile.txt', 'w', function(err, file){
+  if(err) throw err;
+  console.log('opened!');
+})
+
+// write file (replaces the file content if exist with the specified one, if not then new file is created)
+fileSystem.writeFile('createFile.txt', 'Is the content replaced?', function(err){
+  if(err) throw err;
+  console.log('Replaced!');
+})
+
+// Delete files. Method used is unlink
+fileSystem.unlink('createFile.txt', function(err){
+  if(err) throw err;
+  console.log('Deleted!');
+})
+
+// renaming files
+file.rename('createFile.txt', 'renamed.txt', function(err){
+  if(err) throw err;
+  console.log(err);
+})

fileServer2.js

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+// Since now we know how to use url module according to our needs, we will open file and return it 
+// to client parsing the url requested for
+var http = require('http');
+var url = require('url');
+var readFile = require('fs');
+
+// Creating the server
+http.createServer(function (req, res){
+  var query = url.parse(req.url, true);
+  var fileName ='.' + query.pathname;
+  // read the file
+  readFile.readFile(fileName, function(err, data){
+    if(err){
+      res.writeHead('400', {'Content-Type':'text/html'});
+      return res.end("404 NOT FOUND"); // I would encourage you to remove the return keyword from both the places and try
+    }
+    res.writeHead('200', {'Content-Type':'text/html'});
+      res.write(data);
+      return res.end();
+  })
+}).listen(8080);
+

first.js

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+// http is a built-in module here. Think of modules as the libraries in JavaScript.
+// Require function is reuired to include a module.
+var http = require('http');
+
+// Using http module, web server is created
+http.createServer(function (req, res) {
+  res.writeHead(200, {'Content-Type': 'text/html'});
+  res.end('Hello World!');
+}).listen(8080);

operationTest.html

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+<html>
+  <body>
+    <h1> Hello, there</h1>
+    <p> What's going on here? Nothing node.js file system module test</p>
+  </body>
+</html>

readQuery.js

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+var http = require('http');
+
+// create the server. req arguement here represent the request from the client, as an object
+http.createServer(function (req, res) {
+  res.writeHead(200, {'Content-Type': 'text/html'});
+  res.write(req.url); // reads the query and write it to the client
+  res.end();
+}).listen(8080);
+
+// if you run the program with localhost:8080/anyName
+// output should be '/anyName'

splitQuery.js

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+var http = require('http');
+var url = require('url');
+
+http.createServer(function(req, res){
+  res.writeHead(200, {'Content-Type': 'text/html'});
+  var query = url.parse(req.url, true).query;
+  var text = query.year + " " + query.month;
+  res.end(text);
+}).listen(8080);

urlModule.js

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+var url = require('url');
+var address = 'http://localhost:8080/operationTest.htm?year=2017&month=february';
+var query = url.parse(address, true);
+
+console.log(query.hostname); // returns 'localhost:8080'
+console.log(query.pathname); // returns '/operationTest.htm'
+console.log(query.search); // returns '?year=2017&month=february'
+
+var queryData = query.query; // returns an object { year: 2017, month: 'february' }
+console.log(queryData.month); // returns 'february'

useOurModule.js

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+// import http module
+var http = require('http');
+// file name 
+var date = require('./createModules');
+
+// this method is executed when someone tries to access the computer at port 8080
+http.createServer(function  (req, res) {
+  res.writeHead(200, {'content-Type': 'text/html'}); // if the response supposed to be displayed as HTML
+  res.write("Date and time is : " + date.getDateTime()); // Writes the response to the client
+  res.end();// end the response 
+}).listen(8080); // listen to the port at 8080
+
+// remove the writeHead and you will be able to observe the difference in the text