AJAX - The XMLHttpRequest Object
AJAX - More About the XMLHttpRequest Object
Before sending data to the server, we have to explain three important
properties of the XMLHttpRequest object.
The onreadystatechange Property
After a request to the server, we need a function that can receive the data
that is returned by the server.
The onreadystatechange property stores your function that will process the
response from a server. This is not a method, the function is stored in the
property to be called automatically. The following code sets the
onreadystatechange property and stores an empty function inside it:
xmlHttp.onreadystatechange=function()
{
// We are going to write some code here
}
|
The readyState Property
The readyState property holds the status of the server's response. Each time the readyState changes,
the onreadystatechange function will be executed.
Here are the possible values for the readyState property:
| State | Description |
|---|
| 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 |
We are going to add an If statement to the onreadystatechange function to test if
our response is complete (this means that we can get our data):
xmlHttp.onreadystatechange=function()
{
if(xmlHttp.readyState==4)
{
// Get the data from the server's response
}
}
|
The responseText Property
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:
xmlHttp.onreadystatechange=function()
{
if(xmlHttp.readyState==4)
{
document.myForm.time.value=xmlHttp.responseText;
}
}
|
The next chapter shows how to ask the server for some data!
Reliable, affordable, feature-rich web hosting!
Take the uncertainty out of Web hosting and let
GoDaddy.com
put service, performance and value back in. No matter which
hosting type or plan you choose, your site receives 24/7
maintenance and protection in our world-class data center. Plus,
you get the expert, friendly service you deserve, from the
world's largest hostname provider.
With three plans to choose from and
prices starting at just $4.99 per month, GoDaddy.com is sure to have a plan that's
right-sized and right-priced just for you!
All plans feature FREE 24x7 setup, FREE 24x7 monitoring, best-
of-breed routers, firewalls and servers, 24x7 onsite physical security
and access to our exclusive Go Daddy Hosting Connection, THE place
to install over 30 FREE applications. Virtual Dedicated and Dedicated
Server plans also available.
Visit GoDaddy.com today.
Virtual Dedicated, Dedicated Server and unlimited plans also available.
Save 10% on web hosting - Enter code w3tenoff at checkout
 |
|
Get Your Diploma!
W3Schools' Online Certification Program is the perfect solution for busy
professionals who need to balance work, family, and career building.
The HTML Certificate is for developers who want to document their knowledge of HTML, XHTML, and CSS.
The JavaScript Certificate is for developers who want to document their knowledge of JavaScript and the HTML DOM.
The XML Certificate is for developers who want to document their knowledge of XML, XML DOM and XSLT.
The ASP Certificate is for developers who want to document their knowledge of ASP, SQL, and ADO.
The PHP Certificate is for developers who want to document their knowledge of PHP and SQL (MySQL).
|
| 
