JavaScript AJAX Introduction

AJAX Introduction

AJAX stands for Asynchronous JavaScript and XML . AJAX is a dream of every developers because it is used to :

  • Update any web page without reloading/refreshing the page
  • Request data to a server - after the page has loaded
  • Receive data from a server - after the page has loaded
  • Send data to a server in the background without reloading

Simple Example of AJAX

<!DOCTYPE html>
<html>
<body>

     <div id="AjaxDemo">
            <h2>Let's Try  AJAX to change text</h2>
            <button type="button" onclick="ChangeText()">Change Data</button>
     </div>

</body>
</html> 

The HTML page contains a div section having id "AjaxDemo" and a Button. The div section is used to display information received from a server. The Button calls a function "ChangeText()" when it is clicked. The function requests data from a web server and displays it in div id "AjaxDemo"

function ChangeText() 
{
  var xhttp = new XMLHttpRequest();
 
 xhttp.onreadystatechange = function() 
  {
  
  if (this.readyState == 4 && this.status == 200)
    {
        document.getElementById("AjaxDemo").innerHTML = this.responseText;
    }

  };
   
  xhttp.open("GET", "AjaxTest.php", true);
  xhttp.send();
} 

What is AJAX and How it Works ?

AJAX = Asynchronous JavaScript And XML. AJAX is not a programming language. AJAX just uses a combination of

  • A browser built-in XMLHttpRequest object (to request data from a web server)
  • JavaScript and HTML DOM (to display or use the data)

AJAX is a misleading name. AJAX applications might use XML to transport data, but it is equally common to transport data as plain text or JSON text. AJAX allows web pages to be updated asynchronously by exchanging data with a web server behind the scenes. This means that it is possible to update parts of a web page, without reloading the whole page.


Working of AJAX

  • An event occurs in a web page (the page is loaded, a button is clicked)
  • An XMLHttpRequest object is created by JavaScript
  • The XMLHttpRequest object sends a request to a web server
  • The server processes the request
  • The server sends a response back to the web page
  • The response is read by JavaScript
  • Proper action (like page update) is performed by JavaScript