Page 318 - StudyBook.pdf

302 Chapter 5 • Communication Security: Web Based Services

piled into a language that the machine can understand. For this reason, JavaScript is
slower than Java applets.There are both client-side and server-side versions of
JavaScript.
Although JavaScript is different from ActiveX and Java in that it is a scripting
language, it is still possible that a hacker may use a script to acquire information
about a site or use code to attack a site or client computer. However, JavaScript is
generally less likely to cause crashes than Java applets.An important part of
scripting languages like JavaScript and VBScript is that they can run on the client-
side (i.e., on a browser visiting a site) or the server-side (i.e., the Web site itself).
Server-side scripting allows Web pages to provide enhanced features and function-
ality, such as reading and writing to databases, running other programs on the
server, or other operations that couldn’t be performed using client-side scripting.
Running scripts on the server as opposed to the client also has other benefits.
Because the script is executed on the server before any content is provided to the
browser, the script is processed and the results are provided faster than if they ran
on the client-side.
Because server-side scripts are executed on the Web server, it is important that
the code doesn’t have errors that would keep the page from displaying properly, or
not displaying at all. If the script lacked code to handle errors, the Web site may
respond to the error by not displaying the contents of the page.This could occur
when the script tries to access variables or a database that didn’t exist, or any
number of other errors. Similarly, a perpetual loop in the code (where the same
code is run over and over again without exiting) would prevent the script from
running as expected, and prevent the page from loading until the Web server timed
out and ceased execution of the script. By failing to include error handling, scripts
can prevent a user from accessing Web pages, and in the case of a site’s default page,
may prevent users from accessing the site at all.

NOTE

As we’ve mentioned in this chapter, another embedded scripting lan-
guage that you can use in HTML documents is VBScript. As the name
suggests, the syntax of the language looks very similar to Visual Basic,
much like JavaScript resembles Java. It offers approximately the same
functionality as JavaScript in terms of interaction with a Web page, but
a major difference is that VBScript can interact with ActiveX controls
that a user has installed. VBScript is often seen in Active Server Pages
(ASP), as well as in client-side scripts.

www.syngress.com