Java Reference
In-Depth Information
The goal of this module was to make asynchronous requests easier to use, so let's look at a brief code-
only example and see if that goal was accomplished.
The fi rst thing you need is a function to handle the data received from the request; this function gets
passed to the HttpRequest constructor.
function handleData(sResponseText)
{
alert(sResponseText);
}
This code defi nes a function called handleData()that accepts one argument called sResponseText.
When executed, the function merely alerts the data passed to it. Now create an HttpRequest object and
send the request.
var request = new HttpRequest(“http://localhost/myTextFile.txt”, handleData);
request.send();
Pass the text fi le's location and a pointer of the handleData() function to the constructor, and send the
request with the send() method. The handleData() function is called in the event of a successful request.
This module encapsulates the code related to asynchronous XMLHttpRequest requests nicely. You don't
have to worry about creating the request object, handling the readyStateChange event, or checking
the request's status; the HttpRequest module does it all for you.
Validating Form Fields with Ajax
You've probably seen it many times: registering as a new user on a web site's forum or signing up for
web-based e-mail, only to fi nd that your desired user name is taken. Of course, you don't fi nd this out
until after you've fi lled out the entire form, submitted it, and watched the page reload with new data
(not to mention that you've lost some of the data you entered). As you can attest, form validation can be
a frustrating experience; thankfully, Ajax can soften this experience by sending data to the server before
submitting the form — allowing the server to validate the data, and letting the user know the outcome
of the validation without reloading the page!
In this section, you'll create a form that uses Ajax techniques to validate form fi elds. It's possible to
approach building such a form in a variety of ways; the easiest of which to implement provides a link
that initiates an HTTP request to the server application to check whether the user's desired information
is available to use.
The form you'll build will resemble typical forms used today; it will contain the following fi elds:
❑
Username
(validated) — The fi eld where the user types their desired user name
❑
(validated) — The fi eld where the user types their e-mail
Email
❑
Password
(not validated) — The fi eld where the user types their password
❑
Password
(not validated) — The fi eld where the user verifi es their password
Verify
