getdata()

Hello firends

I'm learning ajax ,


From AJAX for dummies:

Quote:

---

Checking to make sure you have
a valid XMLHttpRequest object
Now that you’ve got the needed
XMLHttpRequest object stored in the variable


XMLHttpRequestObject
, how do you actually fetch the text the application
wants when the user clicks the button? All that takes place in the


getData
function in the <script> element, as shown here:

Code:

---

<script language = “javascript”>
.
.
.
function getData(dataSource, divID)
{
.
.
.
}
</script>

---

---

I need to know more about this function.

May someone give me complete example about this function?getdata()?(Its syantax,Tutorial for that...)

GOOD LUCCK!

well I don't have the AJAX for dummies book, but I'll give it a shot.

the getData() javascript method is just an arbitrary name the sample in the book is using. it could be called anything. by looking at the received arguments (datasource,divID) i'd say that datasource is the name of the 'listening' servlet URL (I'm using Java for my example) and divID is the ID of the DIV tag whose contents you are going to replace with the resulting XML response.

your method will construct a URL on the fly, retrieving form parameters the user has entered, or clicked on.
eg:

Code:

---

url= "autocomplete?action=complete&id=" + escape(completeField.value);
var req = initRequest(url);
        req.onreadystatechange = function() {
                       
            if (req.readyState == 4) {
                if (req.status == 200) {
                       
                    parseMessages(req.responseXML);
                } else if (req.status == 204){
                               
                    clearTable();
                }
            }
        };
        req.open("GET", url, true);
        req.send(null);

---

on the other end (java sample) you have a servlet written to receive a 'GET' method, build a query based on the passed in parameters, then construct an XML document from the returned database results. send the XML object back out, add the servlet to your WEB.XML configuration file, and it's ready to roll.

parseMessages() will receive the passed parameter (the XML document returned from the server) and simply construct a DIV tag heirarchy (or whatever you program it to do) that will then replace the innerHTML of the received divID argument. then you can simply allow CSS to position and format the objects rewritten to the document.

Hello firend

thanks for answer

I'm reading another book about AJAX

From AJAX in action page 47

When the user logs in or otherwise initializes a session, several server-side
objects are created, representing, say, the shopping basket and the customer credentials
if this is an e-commerce site. At the same time, the home page is dished
up to the browser, in a stream of HTML markup that mixes together standard
boilerplate presentation and user-specific data and content such as a list of
recently viewed items.
Every time the user interacts with the site, another document is sent to the
browser, containing the same mixture of boilerplate and data. The browser dutifully
throws the old document away and displays the new one, because it is dumb
and doesn’t know what else to do.



"Every time the user interacts with the site, another document is sent to the
browser, containing the same mixture of boilerplate and data. The browser dutifully"

May someone give me example about this?




when We use GET method I know we pass data to URL ,Then Why we need to send boilerplate?why do we need to send HTML?

What is running in AJAX "asynchronous"?Which part are runing "asynchronous"?May someone make it clear by an example?

the server will return an XML file. Typically, you (the developer of the server side script) will DEFINE how the XML is constructed. This makes it a boilerplate. The receiving code will ALWAYS receive the exact same structured XML document. although the data contained within the document might change, the XML structure will always be the same (boilerplate template).

so by this example, I "could" say the boilerplate is (in this instance) simply the STRUCTURE of the XML document.
eg:

Code:

---

<cars>
  <car>red car</car>
  <car>blue car</car>
</cars>

---

and perhaps on the next query:

Code:

---

<cars>
  <car>green car</car>
  <car>white car</car>
  <car>orange car</car>
  <car>blue car</car>
</cars>

---

notice how the structure of the xml document (cars->car) stayed the same (boilerplate template) but the data changed. that's what they mean.

Hello firend ,thanks for answer,

I have anoher question,

From:
http://www.w3schools.com/ajax/ajax_database.asp



The AJAX JavaScript
This is the JavaScript code stored in the file "selectcustomer.js":

var xmlHttp

function showCustomer(str)
{
xmlHttp=GetXmlHttpObject()
if (xmlHttp==null)
{
alert ("Browser does not support HTTP Request")
return
}
var url="getcustomer.asp"
url=url+"?q="+str
url=url+"&sid="+Math.random()
xmlHttp.onreadystatechange=stateChanged
xmlHttp.open("GET",url,true)
xmlHttp.send(null)
}

function stateChanged()
{
if (xmlHttp.readyState==4 || xmlHttp.readyState=="complete")
{
document.getElementById("txtHint").innerHTML=xmlHttp.responseText
}
}

function GetXmlHttpObject()
{
var objXMLHttp=null
if (window.XMLHttpRequest)
{
objXMLHttp=new XMLHttpRequest()
}
else if (window.ActiveXObject)
{
objXMLHttp=new ActiveXObject("Microsoft.XMLHTTP")
}
return objXMLHttp
}




May you explain about this line?

url=url+"&sid="+Math.random()

Why does it create sid?
If we use PHP,Must I do that also?


Thanks in advance.

appending the &sid='+Math.Random() will place a random number at the end of the 'get' request. that makes it seem like a 'unique' url request, and will ensure you always receive a new response from the server (refreshed) rather than your browser displaying a cached response.