Active server pages tutorial: Using ASP and javascript together

Active Server Pages: ASP and Javascript together

In this tutorial we will create a regular HTML page with a small javascript code, and we will use this javascript code to include in the page new information from a ".asp" file.

First, let´s check this two pages:

javascript.html

</body>
</html>

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javascript.asp
document.write ("hello")	1

In the first file (javascript.html) we have include a javascript code in red, and within the code the file name from which we will get information to complete our page (src: source). So that we are asking for information to complete our page (javascript.html) to a different page (javascript.asp). This time we have only include the file name, but we may use the complete url even from a different site (for example: http://www.adifferentsite.com/javascript.asp).

In the second file (javascript.asp) we have include the information necessary to write in the document the word "hello". This time we have use ".asp" extensión for the second page even though other extensions are possible.

The resulting page in our example will be like this one:

javascript.html (resulting page)

hello

So we already know we are able to include a text generated in one page within a different one. As the information we are including can be generate within a ".asp" file, we can add information dinamically by using Active Server Pages.

Let´s try two examples:

A very rudimentary banner rotator system
A simple text hit counter

In case you are using ".asp" files whithin a site and the origen of the information we want to include in the page is originated in the same site, using any of those system is not very convenient: the number of conections to the server will increase, and there may be an important delay. In case you want to include information obtained from an asp script in several pages but you do not want to copy the asp script in all of them, you may use the Include instruction, so that the script is only in one page, and by changing it you will change the results in several pages.

A very rudimentary banner rotator system

Our page is "mypage.html" and we are requesting information to complete it from "http://www.myadrotator.com/adrotator.asp" which may be located in the same or in a different site. The information provided by the second file will determinate the ad to be display in our page.

mypage.html

</body>
</html>

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adrotator.asp

<%
if session("ad")="" then
session("ad")=0
end if

if session("ad")=5 then
session("ad")=1
else
session("ad")=session("ad")+1
end if
%>

<% Select Case session("ad") %>
<% case 1 %>
     document.write ("<A HREF=http://www.1site.com">)
     document.write ("<IMG SCR=1.gif>")
     document.write ("</A>")
<% case 2 %>
     document.write ("<A HREF=http://www.2site.com">)
     document.write ("<IMG SCR=2.gif>")
     document.write ("</A>")
<% case 3 %>
     document.write ("<A HREF=http://www.3site.com">)
     document.write ("<IMG SCR=3.gif>")
     document.write ("</A>")
<% case 4 %>
     document.write ("<A HREF=http://www.4site.com">)
     document.write ("<IMG SCR=4.gif>")
     document.write ("</A>")
<% case 5 %>
     document.write ("<A HREF=http://www.4site.com">)
     document.write ("<IMG SCR=4.gif>")
     document.write ("</A>")
<% End select %>

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Lines 2-3. Each time a new visitor gets to "http://www.myadrotator.com/adrotator.asp" a new session will be open, and by using the session method, we will define session("ad") value to 0. In case the visitor is not new, the value for session("ad") will exits, and that value will be keep.
Lines 6-10. The value for Session("ad") is increased by one unless that value is 5 (which is the maximum value allowed in this script)
Lines 13-34. By using Select_case the page will return the information necessary to display the appropiate ad at "mypage.html". The first time a visitor accesses our page the ad display will be the first one, the second time ad number two and so on. After 5 visits, the process will start again. We may easily increase the number of ads just by adding more obtions within Select_case and setting the maximum number from 5 to the new maximum in line 6.

NOTE: when writing the javascript code you must be very carefull: do not include brakets within the brakets in the javascript code
    p.e.:    Correct: document.write ("<A HREF=http://www.4site.com">)
                Incorrect: document.write ("<A HREF="http://www.4site.com"">)
                Correct: document.write ("<A HREF='http://www.4site.com'">)
    You may include in the response as many lines like the ones above or any other javascript code.

A simple text hit counter

Our page is "mypage.html" and we are requesting information to complete it from "http://www.mycounter.com/hitcounter.asp" which may be located in the same or in a different site. The information provided by the second file will allow to get a text with the number of hits in our page.

mypage.html

</body>
</html>

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hitcounter.asp

<%
Wfile="c:\mydir\cgi-bin\hitcounter.txt"

Set fs = CreateObject("Scripting.FileSystemObject")
Set a = fs.OpenTextFile(Wfile)
hits = Clng(a.ReadLine)
hits = hits + 1
a.close

Set a = fs.CreateTextFile(Wfile,True)
a.WriteLine(hits)
a.Close
%>
document. write ("Number of hits since 2002/01/01: <% =hits %>")

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Lines 2. We will need a text file with a number as its unique content. The path to that file will be openned in variable "Wfile". Creating this page within cgi-bin directory is a good way to prevent visitor from accesing our counter (they will get an error when trying to access a ".txt
file within cgi-bin directory).
Lines 4-8. We will open our file, read the content to a variable ("hits"), and in line 7 the variable will be increased by one.
Lines 10-12 . We will create a new file with the same name (overwriting the previous file) with the content in "hits".
Line 14. The response page will be a javascript code containing the number of hits.

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