Jquery AJAX Introduction

jQuery - AJAX Introduction
AJAX is the art of exchanging data with a server, and updating parts of a web page - without reloading the whole page.
What is AJAX?
AJAX = Asynchronous JavaScript and XML.

In short; AJAX is about loading data in the background and display it on the webpage, without reloading the whole page.
Examples of applications using AJAX: Gmail, Google Maps, Youtube, and Facebook tabs.
You can learn more about AJAX in our AJAX tutorial.

What About jQuery and AJAX?
jQuery provides several methods for AJAX functionality.
With the jQuery AJAX methods, you can request text, HTML, XML, or JSON from a remote server using both HTTP Get and HTTP Post - And you can load the external data directly into the selected HTML elements of your web page!
Without jQuery, AJAX coding can be a bit tricky! Writing regular AJAX code can be a bit tricky, because different browsers have different syntax for AJAX implementation. This means that you will have to write extra code to test for different browsers. However, the jQuery team has taken care of this for us, so that we can write AJAX functionality with only one single line of code.

jQuery AJAX Methods
In the next chapters we will look at the most important jQuery AJAX methods.
jQuery - AJAX load() Method
jQuery load() Method
The jQuery load() method is a simple, but powerful AJAX method.
The load() method loads data from a server and puts the returned data into the selected element.
Syntax:

$(selector).load(URL,data,callback);
The required URL parameter specifies the URL you wish to load.
The optional data parameter specifies a set of querystring key/value pairs to send along with the request.
The optional callback parameter is the name of a function to be executed after the load() method is completed.
Here is the content of our example file: "demo_test.txt":
<h2>jQuery and AJAX is FUN!!!</h2> <p id="p1">This is some text in a paragraph.</p>
The following example loads the content of the file "demo_test.txt" into a specific <div> element:

Example
$("#div1").load("demo_test.txt");
It is also possible to add a jQuery selector to the URL parameter.
The following example loads the content of the element with id="p1", inside the file "demo_test.txt", into a specific <div> element:

Example
$("#div1").load("demo_test.txt #p1");
The optional callback parameter specifies a callback function to run when the load() method is completed. The callback function can have different parameters:
 responseTxt - contains the resulting content if the call succeed
 statusTXT - contains the status of the call
 xhr - contains the XMLHttpRequest object
The following example displays an alert box after the load method() completes. If the load() method has succeed, it displays "External content loaded successfully!", and if it fails it displays an error message:

Example
$("button").click(function(){
$("#div1").load("demo_test.txt",function(responseTxt,statusTxt,xhr){
if(statusTxt=="success")
 alert("External content loaded successfully!");
 if(statusTxt=="error") alert("Error: "+xhr.status+": "+xhr.statusText);
});
});

jQuery - AJAX get() and post() Methods
The jQuery get() and post() methods is used to request data from the server with an HTTP GET or POST request.

HTTP Request: GET vs. POST
Two commonly used methods for a request-response between a client and server are: GET and POST.
 GET - Requests data from a specified resource
 POST - Submits data to be processed to a specified resource
GET is basically used for just getting (retrieving) some data from the server. Note: The GET method may return cached data.
POST can also be used to get some data from the server. However, the POST method NEVER caches data, and is often used to send data along with the request.
To learn more about GET and POST, and the differences between the two methods, please read our HTTP Methods GET vs POST chapter.

jQuery $.get() Method
The $.get() method requests data from the server with an HTTP GET request.
Syntax:

$.get(URL,callback);
The required URL parameter specifies the URL you wish to request.
The optional callback parameter is the name of a function to be executed if the request succeeds.
The following example uses the $.get() method to retrieve data from a file on the server:
Example
$("button").click(function(){
$.get("demo_test.asp",function(data,status){
 alert("Data: " + data + "\nStatus: " + status);
});
});

The first parameter of $.get() is the URL we wish to request ("demo_test.asp").
The second parameter is a callback function. The first callback parameter holds the content of the page requested, and the second callback parameter holds the status of the request.
Tip: Here is how the ASP file looks like ("demo_test.asp"):
<% response.write("This is some text from an external ASP file.") %>

jQuery $.post() Method
The $.post() method requests data from the server using an HTTP POST request.
Syntax:
$.post(URL,data,callback);
The required URL parameter specifies the URL you wish to request.
The optional data parameter specifies some data to send along with the request.
The optional callback parameter is the name of a function to be executed if the request succeeds.

The following example uses the $.post() method to send some data along with the request:
Example
$("button").click(function(){
$.post("demo_test_post.asp", {
name:"Donald Duck", city:"Duckburg"
 },
 function(data,status){
 alert("Data: " + data + "\nStatus: " + status);
 });
});

The first parameter of $.post() is the URL we wish to request ("demo_test_post.asp").
Then we pass in some data to send along with the request (name and city).
The ASP script in "demo_test_post.asp" reads the parameters, process them, and return a result.
The third parameter is a callback function. The first callback parameter holds the content of the page requested, and the second callback parameter holds the status of the request.
Tip: Here is how the ASP file looks like ("demo_test_post.asp"):
<% dim fname,city fname=Request.Form("name") city=Request.Form("city") Response.Write("Dear " & fname & ". ") Response.Write("Hope you live well in " & city & ".") %>

jQuery - The noConflict() Method
What if you wish to use other frameworks on your pages, while still using jQuery?

jQuery and Other JavaScript Frameworks
As you already know; jQuery uses the $ sign as a shortcut for jQuery.
What if other JavaScript frameworks also use the $ sign as a shortcut?
Some other popular JavaScript frameworks are: MooTools, Backbone, Sammy, Cappuccino, Knockout, JavaScript MVC, Google Web Toolkit, Google Closure, Ember, Batman, and Ext JS.
Some of the other frameworks also use the $ character as a shortcut (just like jQuery), and then you suddenly have two different frameworks using the same shortcut, which might result in that your scripts stop working.
The jQuery team have already thought about this, and implemented the noConflict() method.

The jQuery noConflict() Method
The noConflict() method releases the hold on the $ shortcut identifier, so that other scripts can use it.
You can of course still use jQuery, simply by writing the full name instead of the shortcut:
Example
$.noConflict();
 jQuery(document).ready(function(){
jQuery("button").click(function(){
 jQuery("p").text("jQuery is still working!");
});
});

You can also create your own shortcut very easily. The noConflict() method returns a reference to jQuery, that you can save in a variable, for later use. Here is an example:
Example
var jq = $.noConflict();
 jq(document).ready(function(){
 jq("button").click(function(){
jq("p").text("jQuery is still working!");
 });
});

If you have a block of jQuery code which uses the $ shortcut and you do not want to change it all, you can pass the $ sign in as a parameter to the ready method. This allows you to access jQuery using $, inside this function - outside of it, you will have to use "jQuery":

Example
$.noConflict();
 jQuery(document).ready(function($){
 $("button").click(function(){
$("p").text("jQuery is still working!");
 });
});