06/10/2015ajax 1. 2 introduction all material from ajax – what is it? traditional web pages and...

19/04/23 AJAX1

AJAX

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Introduction

All material from www.w3schools.com AJAX – what is it? Traditional web pages and operation Examples of AJAX use Creating an AJAX app AJAX workshop

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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

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Prerequisites

HTML / XHTML JavaScript Knowledge of XML and CSS useful too

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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

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‘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

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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

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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

The XMLHttpRequest object is supported in Internet Explorer 5.0+, Safari 1.2, Mozilla 1.0 / Firefox, Opera 8+, and Netscape 7.

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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

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HTML form below has no submit button

<html> <body> <form name="myForm"> Name: <input type="text" name="username" /> Time: <input type="text" name="time" /> </form>

</body>

</html>

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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

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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

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The XMLHttpRequest object

Has 3 important properties– onreadystatechange– readyState– responseText

The onreadystatechange property stores the function that will process the response from a server

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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

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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

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Here we test the server for response

xmlHttp.onreadystatechange=function() { if(xmlHttp.readyState==4) { document.myForm.time.value=xmlHttp.responseText; } }

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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

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When to send the request

We want to do this when the user releases a key after typing their name

<form name="myForm"> Name: <input type="text" onkeyup="ajaxFunction();" name="username" />

Time: <input type="text" name="time" /> </form>

Calls our function after key released

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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

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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)

<html><body>

<script type="text/javascript">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); }</script>

<form name="myForm">Name: <input type="text"onkeyup="ajaxFunction();" name="username" />Time: <input type="text" name="time" /></form>

</body></html>

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See our AJAX in action

http://engweb.info/ajax/ajaxtest.html Works well in Mozilla IE is a bit sketchy

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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

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References

http://www.w3schools.com/ajax/default.asp http://www.internetnews.com/dev-news/

article.php/3676226 http://daniel.lorch.cc/docs/ajax_simple/

06/10/2015ajax 1. 2 introduction all material from ajax – what is it? traditional web pages and...

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