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What's Wrong With ASP Render blocks?


See what James Shaw from www.CoverYourASP thinks about render blocks. Once you have read this article you will think twice about using them.

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By: James Shaw
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March 07, 2003

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See what James Shaw from www.CoverYourASP thinks about render blocks. Once you have read this article you will think twice about using them.

A simple, normal, ASP page

Consider this simple ASP file below:

<%@ Language=JavaScript %>
<html>
<head>
   <title>My page</title>
</head>
<body>   
We're in "HTML mode" here...
<%
   var sScript = Request.ServerVariables ( "SCRIPT_NAME" );
  
Response.Write ( '<p>I am called ' + sScript + '<p>' );
%>
...and here.
</body>
</html>
 
Most of this file is plain HTML. It is simply streamed out to the browser as-is. The section of JavaScript wrapped in a <% %> is called a render block.

Render blocks aren't a terribly good idea. Many ASP examples out there use them, but I'm going to try and persuade you never to use them again. This may be an uphill struggle!

System Inefficiency

Let's bring out the big guns first. Microsoft doesn't think you should use them. They are inefficient because they force the system to constantly switch back and forth between "HTML mode" and "ASP mode". You know how hard it is to work when your kids are playing in the same room? That's what it's like having to stop and output some HTML when you're busy interpreting script.

Since we're not likely to be writing the next eBay any time soon, that might not be the most relevant argument, so let's try another.

Wasting Bandwidth

You see how the file above is nicely formatted - the <title> tag is indented from the <head> tag? You need to do that when you're coding to make the code easily readable, and hence maintainable.

But you're punishing your users unnecessarily! They have to download your extra line feeds and tabs, when their browser could care less that they are there. The file below renders exactly the same:

<%@ Language=JavaScript %>
<html><head><title>My page</title></head><body>We're in "HTML mode" here...
<%
   var sScript = Request.ServerVariables ( "SCRIPT_NAME" );
   Response.Write ( '<p>I am called ' + sScript + '<p>' );
%>
...and here.</body></html>

 
So, the user is now happier because your page loads faster. If you don't think this matters much do a View/Source on some major sites and see the extra baggage they send out. Remove the HTML comments and the extra spaces/tabs and you'll be surprised how much quicker they download.

I did this exercise on a page generated with FrontPage. It started out as a 40k file - that's a sizeable page to download at 28.8kb. I removed the indentation (which were all spaces) and the HTML comments and the page reduced to 3k. The browser didn't render anything differently, just 10 times quicker!

But what about readability?
Ok, let's say you're with me on the bandwidth issue. But now the code isn't readable, right? Here's the real answer (using my Out function to wrap Response.Write):

<%@ Language=JavaScript %>
<%
// the statement below enables buffering of the data sent to the browser.
// see
http://learnasp.com/learn/whybuffer.asp

%>
<% Response.Buffer=true %>
<%
      Out ( '<html>' );
      Out ( '<head>' );
      Out ( '<title>My page</title>' );
      Out ( '</head>' );
      Out ( 'We're in "HTML mode" here...' );
// output the name of the script itself
      var sScript = Request.ServerVariables ( "SCRIPT_NAME" );
      Out  ( '<p>I am called ' + sScript );
      Out ( '<p>...and here.' );
      Out ( '</body>' );
      Out ( '</html>' );
%>

Indentation, comments, efficiency. What more could you possibly want? You want MORE?

Security

I'm pushing it to say security, but a side-effect of the bandwidth fix is that when everyone in the whole world does a View/Source on your page, they see the almost unintelligible code below. Yes, they can buy a code formatter that will make it look pretty again, but at least admit it's making it more difficult for them?

<html><head><title>My page</title></head><body>We're in "HTML mode" here...<p>I am called temp.asp<p>...and here.</body></html>

Try it now - View/Source - apart from the source code blocks it is just one long line of HTML. (Actually there is one exception. If you have to output an HTML comment add a \n (newline) after it)

It's out there - ASP.NET
My last ditch attempt to persuade you now - ASP.NET. Well it is coming you know, and ASP.NET doesn't allow render blocks that include functions anymore. So this particularly nasty piece of code (IMHO)...

<% function DoSomething ( ) { %>
   something in HTML
<% } %>

...now has to be written like this:

<script language="JavaScript" runat="server">
function DoSomething ( )
{
   Out ( 'something in HTML' );
}
</script>

 
I hope you're convinced now? If not, begone! Back to FrontPage with you...


DISCLAIMER: The content provided in this article is not warranted or guaranteed by Developer Shed, Inc. The content provided is intended for entertainment and/or educational purposes in order to introduce to the reader key ideas, concepts, and/or product reviews. As such it is incumbent upon the reader to employ real-world tactics for security and implementation of best practices. We are not liable for any negative consequences that may result from implementing any information covered in our articles or tutorials. If this is a hardware review, it is not recommended to open and/or modify your hardware.

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