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Web
Crossing Server-side JavaScript
Creating
and Using a JavaScript Function
A
First Example
Troubleshooting
Resources
Next Section
A
First Example
Web Crossing
JavaScript (WCJS) functions reside inside the webx.tpl
file in your Web Crossing folder or directory, as do Web
Crossing Template Language (WCTL) macros.
They can also be kept in separate files and included in the webx.tpl
file the same way macros are.
For our
first example, let's start out by doing something in JavaScript
that you cannot do in WCTL - create a recursive function - a function
which calls itself.
We will
create a factorial function, which is something traditionally
done by programmers writing their first recursive function. Just
to remind you, the factorial of an integer n is
n X (n-1) X (n-2) X .... 1
The factorial
of zero (0!) is defined to be 1.
For example,
the factorial of 4 (written as 4!) is
4 X 3 X 2 X 1 = 24
A complete
JavaScript function to calculate factorial is:
function factorial (n) { if (n == 0) return (1) else return n * factorial(n-1) }
The value
n is passed as a parameter to the factorial function. If the value
of n is 0 then 1 is returned. Otherwise n times the factorial
of n-1 is calculated.
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Note:
Recursive functions are sometimes hard to think about if
you are not used to them. At first they either seem like
magic or your mind starts racing trying to keep up with
what is going on. And if you do not have a good terminating
condition, like the check here to see if n==0, you
could recurse so much that you use up all available memory.
Web Crossing will detect conditions like that to prevent
"blowing your stack". Even if you cannot follow the program
logic in this small example, don't worry about it. What
we are trying to explain here is how to create and use
a JavaScript function inside Web Crossing - not how to do
JavaScript programming. You can still follow the instructions
here and get the function to work. So give it a try!
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To include
this JavaScript function in your Web Crossing server, create a
file called factorial.tpl and enter the following text
in the file:
%% function factorial (n) { if (n == 0) return (1) else return n * factorial(n-1) }%%
By enclosing
the function definition inside the familiar WCTL double-percent
marks, we have done all we need to do to convert a JavaScript
function into Web Crossing readable format.
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Note:
Obviously the %% syntax is required for compatibility with
WCTL. In WCTL, all text
outside %% marks is considered ordinary HTML to be displayed
on the created web page. Defining a function inside %% marks
lets Web Crossing avoid thinking of the function definition
as just ordinary text to be displayed.
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Now move
the factorial.tpl file over to your webx directory,
edit your webx.tpl file there and add the following line
to the beginning or end of the file:
<!--#Include File="factorial.tpl"-->
Finally,
make sure that webx.tpl templates are turned on
and reset the file cache at the bottom of the Control
Panel, as shown in figure 1.
Figure
1 - resetting the file cache
Whenever
you change the contents of webx.tpl or files included in
webx.tpl, you must reset the file cache in order to have
the changes take effect.
Let's
use our new factorial function to calculate 4!. One easy
way to do this is by just calling the function inside a folder
or discussion header. Create a new discussion called JavaScript
Test and place the following WCTL inside the header:
%% "factorial(4)".jsEval %%
Save
your changes and look at what happens when you enter the discussion.
The header should show 24, the value of 4!.
You can
edit the header to change the value inside parentheses and calculate
other factorial values.
The jsEval
command is actually part of WCTL. It is a special command
that allows you to evaluate a character string as though it were
a JavaScript expression, including all your own customized JavaScript
functions. This allows you to freely mix JavaScript in with WCTL
anywhere that WCTL is permitted, even inside WCTL macros.
This
simple example is of limited use because you have to manually
change the value of the number you want to find the factorial
of. The next section will show
you how to create a form that calls a JavaScript function for
processing.
Troubleshooting
I tried
the example above, but when I look at the header all I see is the
code itself, with all the double-percent marks. What am I doing
wrong?
- Make
sure you have turned on WCTL evaluation in the Control
Panels > General Settings:
Resources
Sysop
docs:
Recommended
book:
-
JavaScript - The Definitive Guide, 3rd Edition,
David Flanagan, O'Reilly
This book really is the definitive guide. It
is thorough, readable and answers all your questions about JavaScript.
It is an indispensable resource for any serious JavaScript programmer.
In fact, I won't even recommend any other books. Just get this
one!
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