• Asynchronous JavaScript and XML
• Enables browser to send requests in the background

• HTML, CSS and DOM
• XML
• XMLHttpRequest
• JavaScript

• XMLHttpRequest
• new
• open(method, url, async)
• send()

• GET - retrieve data only
• POST - sending/changing data

• Text or XML
• responseText
• responseXML

• XML
• JSON Example var person = JSON.parse(response)

readyState

• 0 Connection created
• 1 Connection Opened
• 2 Request sent
• 3 Response In Progress
• 4 Request Complete

onreadystatechange

// JavaScript
xhr.setRequestHeader('X-Requested-With', 'XMLHttpRequest');

// PHP
function is_ajax_request() {
	return isset($_SERVER['HTTP_X_REQUESTED_WITH']) && $_SERVER['HTTP_X_REQUESTED_WITH'] == 'XMLHttpRequest';
}

if(is_ajax_request()) {
	echo "Ajax response";
} else {
	echo 'Non-Ajax response';
}

The headers are not secure, can be spoofed.