javascript issue with web.config

Question

trying to access web.config file using js and .net, and get the "error.html?aspxerrorpath=/testing2.aspx" error page.

<%@ Page Language="C#" %>


<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

<html xmlns="http://www.w3.org/1999/xhtml" >
<head runat="server">
    <title>Untitled Page</title>

<script type="text/javascript" runat="server">

    function ReadConfigSettings()
    {

       var v1 = '<%= ConfigurationManager.AppSettings["var1"].ToString() %>'
       alert(v1);

    }
</script>

</head>
<body>
    <form id="form1" runat="server">
   <div><asp:Button ID="Button1" runat="server" Text="Button" OnClientClick="ReadConfigSettings()" /></div>
    </form>
</body>
</html>

Do you have an entry for the key var1 in the appSettings section of your Web.Config file? — Chandu
– Chandu, Commented Apr 19, 2011 at 16:47
this is very dangerous, why don't you provide this value to the function via and ajax call like var v1 = ajax.getVar1(); This don't solve your problem it's just a recomendation. — Rob Alarcon
– Rob Alarcon, Commented Apr 19, 2011 at 16:48
@rob - it's not that dangerous because you're controlling the web.config app setting value. If someone is in there changing that value to something malicious then it's game over anyway wrt to the rest of the site. Also in ASP.NET 4.0 he could use the <%: syntax to Html Encode and sanitise anything malicious. — Kev
– Kev, Commented Apr 20, 2011 at 16:32

Community · Accepted Answer · 2017-05-23 10:33:14Z

1

As rsbarro explained already, your code is probably throwing an exception due to the absence of that setting.

Now, I'm not sure exactly what you are trying to accomplish however. The title of your post, and the code samples seem to indicate you want to extract some value from the config file whenever you click the button. However, that isn't what is happening here.

Remember that anything between <% %> gets evaluated on the server. So before you page ever gets rendered, it will attempt to run that code and embed it into the response as indicated by you. In the end you will get a static value embeded in your script.

<script type="text/javascript" runat="server">

    function ReadConfigSettings()
    {

       var v1 = 'MyStaticValue'; //This was rendered on the server
       alert(v1);

    }
</script>

If you want to do something more than this, then you will have to do this via AJAX. You have a couple of options here:

Create a web service (.asmx, or WCF)
Use Page Methods
Use UpdatePanel

edited May 23, 2017 at 10:33

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answered Apr 19, 2011 at 17:04

Josh

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1 Comment

Dennis Over a year ago

sorry for the confusion, I did create an add key w/ value in the Web.Config file @ the root directory and my goal is to get that value when the form is loaded.

rsbarro · Accepted Answer · 2011-04-19 17:05:55Z

1

Your code example will throw an exception if there is no "var1" defined in the appSettings section.

You could try this instead:

<%= ConfigurationManager.AppSettings["var1"] %>

That statement will handle the case where "var1" is not defined.

To define the appSetting, you should have something like this in your web.config:

<configuration>
   ...
   <appSettings>
      <add key="var1" value="test" />
   </appSettings>
   ...
</configuration>

edited Apr 19, 2011 at 17:05

answered Apr 19, 2011 at 16:49

rsbarro

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1 Comment

Rob Alarcon Over a year ago

something like this <addkey="var1" value="foo"/>

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