Accessing a .NET Webservice via JavaScript

[AlBruAn]

I have a need for a Web Service to retrieve values from a SQL Server database
to populate a dropdown list. That, without any further explanation, sounds
quite simple. The problem is the dropdown list is in FCKeditor, an
open-source WYSIWYG HTML editor written entirely in JavaScript. When the
editor is displayed, I need to query the database based on values selected
from two standard ASP dropdown lists on the page and return the results of
that query to populate the dropdown list in FCKeditor.

Should I write a section of JavaScript in my page to retrieve the selected
indexes of the two ASP dropdown lists once a selection is made and have the
JavaScript function call the Web Service? If so, how do I write the Web
Service to accept the two pieces of information? And how, for that matter,
do I send the message to the Web Service from JavaScript? This thing has me
really confused.

 

[Laurent Bugnion, MVP]

Hi,

I have a need for a Web Service to retrieve values from a SQL Server database
to populate a dropdown list. That, without any further explanation, sounds
quite simple. The problem is the dropdown list is in FCKeditor, an
open-source WYSIWYG HTML editor written entirely in JavaScript. When the
editor is displayed, I need to query the database based on values selected
from two standard ASP dropdown lists on the page and return the results of
that query to populate the dropdown list in FCKeditor.

Should I write a section of JavaScript in my page to retrieve the selected
indexes of the two ASP dropdown lists once a selection is made and have the
JavaScript function call the Web Service?
Yes.

If so, how do I write the Web
Service to accept the two pieces of information?

First, you got to decide if you really want to use a Web Service
(meaning, SOAP) for this quite simple method. Probably it's not the best
idea. SOAP is very bloated, and parsing a SOAP message using pure
JavaScript is quite complex.

The best idea is probably to rather use an ASHX custom handler on the
server, and have it send back some XML data to the calling client. This
is rather simple, see here:
http://www.galasoft.ch/mydotnet/articles/article-2006100601.aspx

And how, for that matter,
do I send the message to the Web Service from JavaScript? This thing has me
really confused.

Unfortunately I never managed to write the article's part two, which is
how to use JavaScript to call the ASHX page you created above.
Thankfully, it's not very complicated. You do this using the
XmlHttpRequest object, which is available in IE, Firefox and other browsers.

To send a request using XmlHttpRequest, you should check the various
tutorials available online.
I recommend:
http://www.ajaxtoolbox.com/

HTH,
Laurent