Node.js

What is Node.js?

Node.js is an open source server environment

Node.js is free

Node.js runs on various platforms (Windows, Linux, Unix, Mac OS X, etc.)

Node.js uses JavaScript on the server

Why Node.js?

A common task for a web server can be to open a file on the server and return the content to the client.

Here is how PHP or ASP handles a file request :

1. Sends the task to the computer's file system.
2. Waits while the file system opens and reads the file.
3. Returns the content to the client.
4. Ready to handle the next request.

Here is how Node.js handles a file request :

1. Sends the task to the computer's file system.
2. Ready to handle the next request.
3. When the file system has opened and read the file, the server returns the content to the client.

Node.js eliminates the waiting, and simply continues with the next request.

Node.js runs single-threaded, non-blocking, asynchronously programming, which is very memory efficient.

What Can Node.js Do?

Node.js can generate dynamic page content

Node.js can create, open, read, write, delete, and close files on the server

Node.js can collect form data

Node.js can add, delete, modify data in your database

What is a Node.js File?

• Node.js files contain tasks that will be executed on certain events
• A typical event is someone trying to access a port on the server
• Node.js files must be initiated on the server before having any effect
• Node.js files have extension ".js"

Install Node.js via NVM

Step 01

        sudo apt-get update

Step 02

        sudo apt-get install build-essential libssl-dev

Step 03

        sudo curl https://raw.githubusercontent.com/creationix/num/v0.33.11/install.sh / bash

   If no curl

            https://raw.githubusercontent.com/creationix/num/v0.33.11/install.sh / bash

Step 04

            source ~/.profile

Step 05 

       nvm --version

Step 06

       nvm install 6.16.0

Step 07

       nvm ls

Step 08      

        node --version

Step 09

        npm --version

What is a Module in Node.js?

• Consider modules to be the same as JavaScript libraries.
• A set of functions you want to include in your application.

Include Modules

• To include a module, use the require() function with the name of the module

 

• Now your application has access to the HTTP module, and is able to create a server

• Now you can include and use the module in any of your Node.js files.

Node.js as a File Server

Common use for the File System module:

1. Read Files
2. Create Files
3. Update Files
4. Delete Files
5. Rename Files

Read Files

The fs.readFile( ) method is used to read files on your computer.

Create Files

The File System module has methods for creating new files:

• fs.appendFile( )

           The fs.appendFile( ) method appends specified content to a file. If the file does not               exist, the file will be created:

           Example:

• fs. open( )

             The fs.open( ) method takes a "flag" as the second argument, if the flag is "w" for                  "writing", the specified file is opened for writing. If the file does not exist, an empty                  file is  created:

            Example:

• fs.writeFile( )

            The fs.writeFile( ) method replaces the specified file and content if it exists. If the 

             file does not exist, a new file, containing the specified content, will be created:

            Example:

Update Files

The File System module has methods for updating files:

• fs.appendFile( )
• fs.writeFile( )

Delete Files

To delete a file with the File System module,  use the fs.unlink( ) method.

• fs.unlink( )

Rename Files

To rename a file with the File System module,  use the fs.rename( ) method.

• fs.rename( )

Upload Files

Step 1 : Create an Upload Form

Example :

var http = require('http');

http.createServer(function (req, res) {
  res.writeHead(200, {'Content-Type': 'text/html'});
  res.write('<form action="fileupload" method="post" enctype="multipart/form-data">');
  res.write('<input type="file" name="filetoupload"><br>');
  res.write('<input type="submit">');
  res.write('</form>');
  return res.end();
}).listen(8080);

Step 2 : Parse the Uploaded File

• Include the Formidable module to be able to parse the uploaded file once it reaches the server.
• When the file is uploaded and parsed, it gets placed on a temporary folder on your computer.

Example :

var formidable = require('formidable');

http.createServer(function (req, res) {
  if (req.url == '/fileupload') {
    var form = new formidable.IncomingForm();
    form.parse(req, function (err, fields, files) {
      res.write('File uploaded');
      res.end();
    });
  } else {
    res.writeHead(200, {'Content-Type': 'text/html'});
    res.write('<form action="fileupload" method="post" enctype="multipart/form-data">');
    res.write('<input type="file" name="filetoupload"><br>');
    res.write('<input type="submit">');
    res.write('</form>');
    return res.end();
  }
}).listen(8080);

Step 3 : Save the File

• When a file is successfully uploaded to the server, it is placed on a temporary folder.
• The path to this directory can be found in the "files" object, passed as the third argument in the parse( ) method's callback function.
• To move the file to the folder of your choice, use the File System module, and rename the file:

Example :

var http = require('http');
var formidable = require('formidable');
var fs = require('fs');
http.createServer(function (req, res) {
  if (req.url == '/fileupload') {
    var form = new formidable.IncomingForm();
    form.parse(req, function (err, fields, files) {
      var oldpath = files.filetoupload.path;
      var newpath = 'C:/Users/Your Name/' + files.filetoupload.name;
      fs.rename(oldpath, newpath, function (err) {
        if (err) throw err;
        res.write('File uploaded and moved!');
        res.end();
      }); });
  } else {
    res.writeHead(200, {'Content-Type': 'text/html'});
    res.write('<form action="fileupload" method="post" enctype="multipart/form-data">');
    res.write('<input type="file" name="filetoupload"><br>');
    res.write('<input type="submit">');
    res.write('</form>');
    return res.end();
  }
}).listen(8080);