Initializing JavaScript Variables on Server Side

Question

I am having problems setting JavaScript variables on the Server Side in ASP.Net Web Forms (Not MVC) using Master Pages.

Basically I want to do something like this:

<script type="text/javascript">
    var z = '<%# Request.QueryString["Env"] %>';
</script>

After I run the code I see: var z=’’;

I also tried:

var z = '<%= Request.QueryString["Env"] %>';

After I run that code I get the following error so I assume that is not correct:

The Controls collection cannot be modified because the control contains code blocks (i.e. <% ... %>).

I have been doing mainly MVC development these past few years so I am not sure what I am doing wrong.

Please let me know.

Thanks

I have been away from WebForms for a while also but your second snippet looks like what I remember. Can you post a bit more of the surrounding code? — Matthew Nichols
– Matthew Nichols, Commented Jan 28, 2012 at 14:09
Dynamic javascript is a known anti pattern. Don't do this shit. — Raynos
– Raynos, Commented Jan 28, 2012 at 14:34
@Raynos: I guess you don't do a lot of MVC development since it is used all over the place. — Richard
– Richard, Commented Jan 29, 2012 at 20:04
@RichardCorkery I know anti patterns are used all over the place. That's because most developers don't know what they are doing. I'm not surprised anything to do with ASP.NET is full of anti patterns — Raynos
– Raynos, Commented Jan 29, 2012 at 20:21

chandmk · Accepted Answer · 2012-01-28 15:03:38Z

3

I think it is a good idea to place the javascript just before closing the body tag instead of head tag. Then you can use <%= syntax.

answered Jan 28, 2012 at 15:03

chandmk

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1 Comment

Richard Over a year ago

Thanks for responding. I used this option and it worked. Thanks.

Rey Rahadian · Accepted Answer · 2012-01-28 14:32:44Z

1

any chance that the javascript block you mention is inside a server control ?

for example :

<head runat="server">
  <script type="text/javascript">
    var z = '<%# Request.QueryString["Env"] %>';
  </script>
<head>

if so try changing it to :

 <head runat="server">
    <div runat="server">
      <script type="text/javascript">
        var z = '<%= Request.QueryString["Env"] %>';
      </script>
    </div>
 <head>

reference : http://www.west-wind.com/weblog/posts/2006/May/27/The-Controls-collection-cannot-be-modified-because-the-control-contains-code-blocks-ie-

edited Jan 28, 2012 at 14:32

answered Jan 28, 2012 at 14:09

Rey Rahadian

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Comments

Aristos · Accepted Answer · 2012-01-28 14:15:46Z

0

For sure the <%# %> is for iteration, to render a string you need to use <%= %> how ever because is probably on the header that runs on server is better to avoid that and use a literal like that.

<script type="text/javascript">
    <asp:literal run="server" id="txtJavaDeclarations" EnableViewState="false" />
</script>

on code behind

txtJavaDeclarations.Text 
      = string.Format("var z = '{0}' ;\n", Request.QueryString["Env"]);

answered Jan 28, 2012 at 14:15

Aristos

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Comments

Crab Bucket · Accepted Answer · 2012-01-28 14:53:01Z

0

I would be tempted to use

ClientScript.RegisterClientScriptBlock(GetType(), "scriptBlockKey", 
        "var z = '" + Request.QueryString["Env"] + "';", true);

That should write in the script block you need with the script tags (final argument set to true).

It's called from the server side so just pop it in Page_Load. It's got the benefit of being easier to debug is things go wrong.

I would be tempted to to a null check on the query string as well with a tenary operator i,e,

  string env = Request.QueryString["Env"] == null ? string.Empty : 
                                    Request.QueryString["Env"].ToString();
    ClientScript.RegisterClientScriptBlock(GetType(), "scriptBlockKey", 
            "var z = '" + env + "';", true);

Just makes the null check a bit more transparent and perhaps gives the opportunity for a default case.

edited Jan 28, 2012 at 14:53

answered Jan 28, 2012 at 14:14

Crab Bucket

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1 Comment

Richard Over a year ago

Thanks for responding. I used this option and it worked. However, I decided to go with a different Answer to solve my problem since it was a little less changes. Thanks again.

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