Node js tutorial - What is node js - learn node js

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What is NodeJS :

• Node.js lets us use JavaScript language on the server… so it allows us to write JavaScript outside the browser!
• Node.js has all the power of JavaScript and offers us a whole new way of developing dynamic websites.

• Asynchronous Event Driven Server Side JavaScript
• Non-blocking I/O and File API
• Runs on Google JS V8 Engine
• Single Threaded
• Highly Scalable
• Node Apps are created using JavaScript
• Faster in performance

• 1.Multiple requests are sent to the Node.js server.
• 2.The event-driven nature of Node.js creates a loop of events for all requests and handles them under a single thread.
• 3.These events are then delegated to the appropriate non-blocking event handler.
• 4.The response received travels the reverse way to the requested end point.
• 5.Since the process happens under a single thread, the response is sent asynchronously without causing page refresh.

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Explain NodeJS :

• An open-source runtime environment that contains JavaScript code for execution in the server to aid in asynchronous request-response strategy.
• A library with variety of modules needed for network and web application development.
• Is developed by Ryan Dahl in 2009.
• Is part of V8 JavaScript, a Google's implementation for the Chrome browser, with "Just in Time" compilation services to achieve high speeds for executions.
• Uses a non-blocking, event-driven I/O environment to handle high-critical real-time applications running across distributed devices.
• Prevents its applications from data buffers, regardless of its extended service processing tasks

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History of NodeJS :

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How webpage works :

How webpage works

how nodejs works :

• Node.js offers a server-side environment, which allows us to also use JavaScript language to generate web pages. Basically, it replaces server languages such as PHP, Java EE, etc.

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Blocking model vs. non-blocking model :

• Considering a program, which upload a file and then display it. Below is the code written in a blocking model:
• Upload the file
• Display the file
• Do something else

• The actions are carried out in top to bottom order.
• The program will upload a file to the Internet.
• The program will display the file to the user.
• Then, the program can do other things (i.e. carry out other actions).

• Lets see the same code in a non-blocking model:
• Upload a file
• As soon as it’s finished, display the file
• Do something else

• The program wont carry out the tasks in the order that they are written. It does this:
• The program launches the upload of the file to the internet.
• The program does other things (the program follows its course).
• As soon as the upload is finished, the program carries out the actions that we asked it to do: it displays the file.

On the whole, the running of the program can therefore be represented as in the next figure.

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This is exactly how Node.js works. As soon as "File uploaded" appears, a function known as a callback function is called and carries out actions (here, the callback function displays the file).

  // // Identical result to the previous code

var callback = function (error, response, body) {
console.log ("Hey Wikitechy File uploaded!");
});

request (‘http://www.site.com/file.zip',callback);

console.log ("I do other things while I’m waiting… "); 

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nodejs sample code :

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• Line 1
• Loading http module
• It is required to work with HTTP request and response
• It is required to create HTTP Server

• Line 2
• Create server using createServer() function
• It takes a callback as parameter . It takes HTTP request and response as paramtere
• Callback got two input parameter .
• Both input parameters are readable and writeable stream

• Line 4
• Writing response header
• It takes a JSON object as optional second parameter
• second parameter contains informations like
• Content Length
• Content Type
• Connection
• Accept Type

• Line 5-6
• Writing data in response
• Data can be written in form of string or buffer
• ServerResponse.end indicates the communication has been finished

• Line 9
• createServer() method is finished with chained http.Server.listen() method
• It specifies port number on which request will be listen Optional host name

• Line 10
• Printing a message

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nodejs workflow :

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• It works on single thread
• It handles all request asynchronously on same thread
• It does not create new thread for each request which is very unlikely like other web servers
• It does not wait to complete a request

node js - Asynchronous Vs Event-Driven :

• Asynchronous code execution -
• Not all code is executed in the same order it is written
• Node (and you) divide the code into small pieces and fire them in parallel
• Typically the code announces its state of execution (or completion) via events
• Event-Driven code execution -
  • A code block gets into the queue of execution when an event happens
  ------------- It gets executed on its turn
  • Anyone can raise (or listen to) an event
  ------------- System
  ------------- Some library (module)
  ------------- Your code
  • You have the choice (and ways) to attach a code block to an event
  ------------- Also known as event callbacks