06/10/2015AJAX 1

2 Introduction All material from AJAX – what is it? Traditional web pages and operation Examples of AJAX use Creating an AJAX app AJAX workshop

AJAX 3 AJAX – the basics AJAX stands for Asynchronous JavaScript And XML Based on JavaScript and HTTP requests AJAX is a type of programming made popular in 2005 by Google (with Google Suggest) AJAX is not a new programming language, but a new way to use existing standards AJAX is good for creating better, faster, and more user-friendly web applications

AJAX 4 Prerequisites HTML / XHTML JavaScript Knowledge of XML and CSS useful too

AJAX 5 How AJAX works With AJAX, your JavaScript can communicate directly with the server, using the JavaScript XMLHttpRequest object. With this object, your JavaScript can trade data with a web server, without reloading the page AJAX uses asynchronous data transfer (HTTP requests) between the browser and the web server, allowing web pages to request small bits of information from the server instead of whole pages. The AJAX technique makes Internet applications smaller, faster and more user-friendly. AJAX is a browser technology independent of web server software

AJAX 6 ‘Old’ way of getting/ sending data In traditional JavaScript coding, to fetch or send information to or from a database or a file on webserver requires making an HTML form and GET or POST data to the server User clicks "Submit" button to send/get the information, waits for the server to respond, then a complete new page loads with results Since server returns a new page each time user submits input, traditional web apps can run slowly and tend to be less user-friendly

AJAX 7 AJAX Uses HTTP Requests AJAX means JavaScript communicates directly with server, using JavaScript XMLHttpRequest object With an HTTP request, web page can make a request to, and get a response from a web server - without reloading the entire page The user remains on same page Does not notice that scripts request pages, or send data to a server in the background Greater transparency – better user experience

Dec 2007AJAX 8 The XMLHttpRequest Object By using the XMLHttpRequest object, a web developer can update a page with data from the server after the page has loaded AJAX was made popular in 2005 by Google (with Google Suggest). Google Suggest uses the XMLHttpRequest object to create a very dynamic web interface: When you start typing in Google's search box, a JavaScript sends the letters off to a server and the server returns a list of suggestions Google Suggest The XMLHttpRequest object is supported in Internet Explorer 5.0+, Safari 1.2, Mozilla 1.0 / Firefox, Opera 8+, and Netscape 7.

AJAX 9 Your First AJAX Application To understand how AJAX works, we will create a small AJAX application First, we are going to create a standard HTML form with two text fields: username and time The username field will be filled in by the user and the time field will be filled in using AJAX. The HTML file will be named "testAjax.htm See next slide

AJAX 10 HTML form below has no submit button Name: Time:

AJAX 11 AJAX - Browser Support The keystone of AJAX is the XMLHttpRequest object Different browsers use different methods to create the XMLHttpRequest object We don’t know which browser any user may use Internet Explorer uses an ActiveXObject, while other browsers uses the built-in JavaScript object called XMLHttpRequest To create this object, and deal with different browsers, we are going to use a "try and catch" statement

function ajaxFunction() { var xmlHttp; try { // Firefox, Opera 8.0+, Safari xmlHttp=new XMLHttpRequest(); } catch (e) { // Internet Explorer try { xmlHttp=new ActiveXObject("Msxml2.XMLHTTP"); } catch (e) { try { xmlHttp=new ActiveXObject("Microsoft.XMLHTTP"); } catch (e) { alert("Your browser does not support AJAX!"); return false; } } } } Script creates variable Comments Warning for user if all browsers fail IE can use 2 types of ActiveXObjects

Dec 2007AJAX 13 Code needed to make AJAX run Tries to create the XMLHttpRequest object Check non-IE browsers first If the test fails, code first tries newer then older IE versions Returns error message for very old browsers Can be cut and paste into your AJAX page

Dec 2007AJAX 14 The XMLHttpRequest object Has 3 important properties – onreadystatechange – readyState – responseText The onreadystatechange property stores the function that will process the response from a server

Dec 2007AJAX 15 readyState The readyState property holds the status of the server's response. We can use this to execute the onreadystatechange function Possible values for the readyState property: – 0 The request is not initialized – 1 The request has been set up – 2 The request has been sent – 3 The request is in process – 4 The request is complete

Dec 2007AJAX 16 responseText The data sent back from the server can be retrieved with the responseText property. In our code, we will set the value of our "time" input field equal to responseText

Dec 2007AJAX 17 Here we test the server for response xmlHttp.onreadystatechange=function() { if(xmlHttp.readyState==4) { document.myForm.time.value=xmlHttp.responseText; }

Dec 2007AJAX 18 Sending a request to a server To send off a request to the server, we use the open() method and the send() method The open() method takes three arguments – The first argument defines which method to use when sending the request (GET or POST) – The second argument specifies the URL of the server-side script – The third argument specifies that the request should be handled asynchronously (true or false) The send() method sends the request off to the server

Dec 2007AJAX 19 When to send the request We want to do this when the user releases a key after typing their name Name: Time: Calls our function after key released

Dec 2007AJAX 20 Forming a changing server-side file We will fetch the time from our server Use php to deal with time request Simple server-side file

Dec 2007AJAX 21 Fetching the time We fetch time from a remote server’s php ajaxtest.php Place that in the code Save the file as html Place on your web server in same directory as php file Bingo – page works (only with IE just now)

function ajaxFunction() { var xmlHttp; try { // Firefox, Opera 8.0+, Safari xmlHttp=new XMLHttpRequest(); } catch (e) { // Internet Explorer try { xmlHttp=new ActiveXObject("Msxml2.XMLHTTP"); } catch (e) { try { xmlHttp=new ActiveXObject("Microsoft.XMLHTTP"); } catch (e) { alert("Your browser does not support AJAX!"); return false; } xmlHttp.onreadystatechange=function() { if(xmlHttp.readyState==4) { document.myForm.time.value=xmlHttp.responseText; } xmlHttp.open("GET","ajaxtest.php",true); xmlHttp.send(null); } Name: <input type="text" onkeyup="ajaxFunction();" name="username" /> Time:

Dec 2007AJAX 23 See our AJAX in action Works well in Mozilla IE is a bit sketchy

Dec 2007AJAX 24 Conclusion AJAX extends the usefulness of web apps Saves entire pages reloading Gives greater transparency to users Data loads ‘in the background’ Uses existing technologies Is becoming very popular

Dec 2007AJAX 25 References news/article.php/ news/article.php/