I will try to describe this issue by taking a case of changing the Magento’s login functionality to a Ajax powered login functionality. So after this you will be able to implement a login function in a pop-up div in any page, unlike the default Magento’s seperate login page. I will leave the pop-up div part to you and get started with the real business (AJAX and JSON).

Presuming that you will use Mini-Login form. Here is how you proceed.

1. Change Submit type button to Button type button.
2. Register OnClick Javascript event of that button and its Handler
3. In the Handler function call Ajax Request for login
4. Show Error Message or redirect to customer Dashboard

Your mini.login.phtml should be like this

<form action="<?php //echo $this->getPostActionUrl() ?>" id="mini-login-form" method="post">
    <fieldset>
        <p><label><?php echo $this->__('Email') ?>:</label> <input name="login[username]" class="input-text" /></p>
        <p><label><?php echo $this->__('Password') ?>:</label> <input name="login[password]" class="input-text" /></p>
        <p><input type="button" onClick="handlerFunction()" value="<?php echo $this->__('Login') ?>" /></p>
    </fieldset>
</form>

<script type="text/javascript">
<!--
function handlerFunction(){

// Write These codes only after form Validation

// Making Ajax Request
		var request = new Ajax.Request(
			//Defining Ajax Request URL, We are calling custom Controller Ns_Mylogin_AccountController Class (Defined Below)
        	'<?php echo $this->getUrl("mylogin/account/loginPost") ?>',
           	{
            	method: 'post',
                onComplete: function(transport){ // Defining Complete Callback Function

                	// Getting Ajax Response Text Which is JSON Object
                	var jsonResponse=transport.responseText;
                	//Checking JSON Objects property and performing related action
                	// You will understand the response Text format after going through the controller description (Below)
                	if(jsonResponse.error){
                		alert("Error Occured");
						return false;
                	}
                	else{
                		window.location.href=jsonResponse.url;
                	}
                },
                parameters: Form.serialize($("mini-login-form"))	// Seriallizing the form input values
        	}
        );
}
//-->
</script>

Please see inline comments for better understanding. Now our next set should be setting up our custom controller. I’ll not get into details of setting up modules and all but directly to our controller class Ns_Mylogin_AccountController. What I’ve done is just taken the core’s loginPostAction function of Mage_Customer_AccountController and added some codes there. Please see there is a comment on each line added apart from the default Magento’s core code.

<?php
require_once("Mage/Customer/controllers/AccountController.php");
class Ns_Mylogin_AccountController extends Mage_Customer_AccountController{
	/**
	 * Login post action
	 * @return JSON Object
	 */
	public function loginPostAction()
	{
		// Added Line #1
		$result["error"]=0;

		$session = $this->_getSession();

		if ($this->getRequest()->isPost()) {
			$login = $this->getRequest()->getPost('login');
			if (!empty($login['username']) &amp;&amp; !empty($login['password'])) {
				try {
					$session->login($login['username'], $login['password']);
					if ($session->getCustomer()->getIsJustConfirmed()) {
						$this->_welcomeCustomer($session->getCustomer(), true);
					}
				} catch (Mage_Core_Exception $e) {
					switch ($e->getCode()) {
						case Mage_Customer_Model_Customer::EXCEPTION_EMAIL_NOT_CONFIRMED:
							//Added Line #2
							$result["error"]=1;
							$message = Mage::helper('customer')->__('This account is not confirmed. <a href="%s">Click here</a> to resend confirmation email.', 						Mage::helper('customer')->getEmailConfirmationUrl($login['username']));
							break;
						case Mage_Customer_Model_Customer::EXCEPTION_INVALID_EMAIL_OR_PASSWORD:
							//Added Line #3
							$result["error"]=1;
							$message = $e->getMessage();
							break;
						default:
							//Added Line #4
							$result["error"]=1;
							$message = $e->getMessage();
					}
					$session->addError($message);
					$session->setUsername($login['username']);
				} catch (Exception $e) {
					// Mage::logException($e); // PA DSS violation: this exception log can disclose customer password
				}
			} else {
				//Added Line #5
				$result["error"]=1;
				$session->addError($this->__('Login and password are required'));
				//Added Line #6
				$this->getResponse()->setBody(Mage::helper('core')->jsonEncode($result));
			}
		}
		//Added Line #7
		$result["url"]=$this->_loginPostRedirect();
		//Added Line #8
		$this->getResponse()->setBody(Mage::helper('core')->jsonEncode($result));
	}

What I’ve done is added an array $result that will hold value if there is error or not while processing the user’s request. If there is error that array will hold $result['error']=1 else it will be as initiallized in Added Line #1. From Added Line #2 through Added Line #5, we have various condition to check for error and set our $result variable.

On Added Line #7 we have called another function (which we we rewrite as well) that will give us the url location identifying which location should be redirect after successful login. The implementation of function is given below. Finally in Added Line #8 and Line #6 we have encoded our $result array into JSON format and send as the response.

For visuallization our $result array will be one of the following.

1. Case (No Error) : $result["error"]=0; $result["url"]=”SOME Redirect URL”
2. Case (Error) : $result["error"]=1;

This JSON encoded response will be then used by the ajax call back function defined and perform related action.

Here’s the _loginPostRedirect() function which I mentioned (Added Line #7).

/**
	 * Define target URL and redirect customer after logging in
	 */
	protected function _loginPostRedirect()
	{
		$session = $this->_getSession();

		if (!$session->getBeforeAuthUrl() || $session->getBeforeAuthUrl() == Mage::getBaseUrl() ) {

			// Set default URL to redirect customer to
			$session->setBeforeAuthUrl(Mage::helper('customer')->getAccountUrl());

			// Redirect customer to the last page visited after logging in
			if ($session->isLoggedIn())
			{
				if (!Mage::getStoreConfigFlag('customer/startup/redirect_dashboard')) {
					if ($referer = $this->getRequest()->getParam(Mage_Customer_Helper_Data::REFERER_QUERY_PARAM_NAME)) {
						$referer = Mage::helper('core')->urlDecode($referer);
						if ($this->_isUrlInternal($referer)) {
							$session->setBeforeAuthUrl($referer);
						}
					}
				}
				else if ($session->getAfterAuthUrl()) {
					$session->setBeforeAuthUrl($session->getAfterAuthUrl(true));
				}
			} else {
				$session->setBeforeAuthUrl(Mage::helper('customer')->getLoginUrl());
			}
		} else if ($session->getBeforeAuthUrl() == Mage::helper('customer')->getLogoutUrl()) {
			$session->setBeforeAuthUrl(Mage::helper('customer')->getDashboardUrl());
		}
		else {
			if (!$session->getAfterAuthUrl()) {
				$session->setAfterAuthUrl($session->getBeforeAuthUrl());
			}
			if ($session->isLoggedIn()) {
				$session->setBeforeAuthUrl($session->getAfterAuthUrl(true));
			}
		}
		// Changed Here
		return $session->getBeforeAuthUrl(true);
	}

You can download the code From Here.

Hope it helps! Happy Coding.

Controller: The url on which Ajax will work on, or the request URL. You will have to set up the controller with its frontend router set in config.xml and its corresponding controller class.
Layout: Layout to handle the requested URL and return HTML if required.
Block: The block to call through layout for the above controller.

Now lets be descriptive.

If you want to show a loader while request is being processed just add the following whereever you like in the phtml page.First fetch the Javascript.

<script src="<?php echo $this->getJsUrl() ?>mage/adminhtml/loader.js" type="text/javascript"></script>

Then echo the loader which pops up. This loader will be similar to that of the admin.

<div id="loadingmask" style="display: none;">
<div class="loader" id="loading-mask-loader"><img src="<?php echo str_replace("index.php/","",$this->getUrl()) ?>skin/adminhtml/default/default/images/ajax-loader-tr.gif" alt="<?php echo $this->__('Loading...') ?>"/><?php echo $this->__('Loading...') ?></div>
<div id="loading-mask"></div>
</div>

Now to Call Ajax, use the following lines

/*Please note that the URL is created in reloadurl. Also see that the response text will be echoed in div with id=output-div*/

var reloadurl = '<?php echo $this->getUrl('router/controller/action') ?>';
Element.show('loadingmask');
new Ajax.Request(reloadurl, {
method: 'post',
parameters: "Params_Here",
onComplete: function(transport) {
Element.hide('loadingmask');
$('output-div').innerHTML = "";
$('output-div').innerHTML = transport.responseText;

}
});

After the Ajax Request is made it goes to your controller’s action, which in turn sees to your layout as follows:

class Namespace_module_frontendController extends Mage_Core_Controller_Front_Action
{
public function actionAction(){
$this->loadLayout()->renderLayout();
}
}

And here is the main part in layout where I spent most of my time in. Since in layout we will have to define reference where the html will echo (Most of the times), i got stuck here, because i need to echo the output on the div with id output-div not in any reference.And the trick is to name the layout as root and output as html. Like the following:

<module_controller_action>
<block type="module/block"  name="root" output="toHtml"  template="module/template.phtml"/>
</module_controller_action>

You are done now! What ever you write or echo in phtml file you will see populated in the DIV. Now you can treat block as normally as you do before.

Happy Coding!!

<form action="iframeinc.php" method="post" enctype="multipart/form-data" id="uploadform" target="iframe" name="uploadform">
 File:
  <input name="pic" type="file" id="pic" style="margin-right:50px;" />
  <br />
<input type="submit" name="Submit" value="Upload" ><br />
<iframe name="iframe" src="iframeinc.php" width="200" height="500" style="display:none;"> </iframe>
</form>

You can see on #1 the action of the form is iframeinc.php. The code for this page is given below. There are some other things you should remember. Like the target for the form is set iframe, whose display is set none so that it is not seen. And this iframe is the of the iframe created on #6, whose source is the iframeinc.php. Now here’s its code.

<?php
if($_POST){

	// $newname is the new path/name of the file on the server.
	$copied = copy($_FILES['pic']['tmp_name'], "$newname");

}
?>

Remember to set $newname value before running this. At first run you may see this as a regular post script, but try to reload with f5 or reload button of your browser, you will not be asked to retry or resend the post header. So, there are own ways of catching your nose.
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