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AJAX

AJAX. Quick Introduction. AJAX = Asynchronous JavaScript A nd XML. What is AJAX, actually?. Ajax isn’t a technology. It’s really several technologies, each flourishing in its own right, coming together in powerful new ways. Ajax incorporates:

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AJAX

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  1. AJAX Quick Introduction

  2. AJAX =AsynchronousJavaScriptAndXML

  3. What is AJAX, actually? • Ajax isn’t a technology. It’s really several technologies, each flourishing in its own right, coming together in powerful new ways. Ajax incorporates: • standards-based presentation using XHTML and CSS; • dynamic display and interaction using the Document Object Model; • data interchange and manipulation using XML and XSLT; • asynchronous data retrieval using XMLHttpRequest; • and JavaScript binding everything together.

  4. How Ajax is Different • An Ajax application eliminates the start-stop-start-stop nature of interaction on the Web by introducing an intermediary — an Ajax engine — between the user and the server. It seems like adding a layer to the application would make it less responsive, but the opposite is true. • Instead of loading a webpage, at the start of the session, the browser loads an Ajax engine — written in JavaScript and usually tucked away in a hidden frame. This engine is responsible for both rendering the interface the user sees and communicating with the server on the user’s behalf. • The Ajax engine allows the user’s interaction with the application to happen asynchronously — independent of communication with the server. So the user is never staring at a blank browser window and an hourglass icon, waiting around for the server to do something.

  5. Is AJAX production-ready? • The biggest challenges in creating Ajax applications are not technical. The core Ajax technologies are mature, stable, and well understood. Instead, the challenges are for the designers of these applications: to forget what we think we know about the limitations of the Web, and begin to imagine a wider, richer range of possibilities.

  6. How does it look in code? • Step 1 –How to Make an HTTP Request • var httpRequest; • if (window.XMLHttpRequest) { // Mozilla,Safari, ...httpRequest = new XMLHttpRequest(); } • else if (window.ActiveXObject) { // IE httpRequest = new ActiveXObject("Microsoft.XMLHTTP"); }

  7. How does it look in code? • Step 2 – Handling server response • if (httpRequest.readyState == 4) { // everything is good, the response is received } • else { // still not ready }

  8. How does it look in code? • A simple example • The user clicks the link "Make a request" in the browser; • This calls the makeRequest() function with a parameter – the name test.html of an HTML file in the same directory; • The request is made and then (onreadystatechange) the execution is passed to alertContents(); • alertContents() checks if the response was received and it's an OK and then alert()s the contents of the test.html file.

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