ASP.NET C#: JavascriptSerializer could not be found

Question

I'm trying to use the JavascriptSerializer object in ASP.NET v4.0 with C#. I'm not using Visual Studio--this is on a live IIS7 server. I can access this object just fine using VB on this same web server, so I know the requisite DLLs are present and correctly configured.

But when I try to use this object in C#, I get this error: The type or namespace name 'JavascriptSerializer' could not be found

In my class file, I have this:

using System.Web;
using System.Web.Script;
using System.Web.Script.Serialization;

In web.config, I have this:

<assemblies>
    <add assembly="System.Web.Extensions, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35" />
</assemblies>

In my default.aspx.cs file, I have this:

JavaScriptSerializer obj_serializer = new JavascriptSerializer();

It's this last line of code that is causing the above referenced error.

Help?

Cameron Tinker · Accepted Answer · 2013-04-04 17:56:17Z

16

You need to add a reference to System.Web.Extensions.dll in your application. System.Web.Extensions is the namespace that contains the JavaScriptSerializer class. Then add a using directive to use the namespace System.Web.Extensions like so:

using System.Web.Extensions;

You can also declare your JavaScriptSerializer like this:

var serializer = new System.Web.Extensions.JavaScriptSerializer();

answered Apr 4, 2013 at 17:56

Cameron Tinker

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T.Todua · Accepted Answer · 2018-03-13 16:43:51Z

4

Instead you might need:

using System.Web.Script.Serialization;

answered Mar 13, 2018 at 16:43

T.Todua

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Zavi · Accepted Answer · 2019-08-19 08:56:53Z

4

To Solve The Problem -> Just Take reference Step->BY->Step

1.-> Go To Reference of Your project File.

2.-> Right click Then Go To Add Reference

3.-> Go To Framework

4.-> Then Take The Reference--->System.Web.Extensions

5.-> Problem Solved.

edited Aug 19, 2019 at 8:56

Zavi

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answered Aug 19, 2019 at 8:21

Sabuj Sarker

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Cameron · Accepted Answer · 2013-04-04 17:58:25Z

3

I don't know if you just incorrectly typed the line, but it's JavaScriptSerializer, not JavascriptSerializer (Capital S in Script).

answered Apr 4, 2013 at 17:58

Cameron

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4 Comments

Octavient Over a year ago

Thank you so much. I keep forgetting that C# is case sensitive (been stuck in VB for several years now)...

Moby's Stunt Double Over a year ago

Ha! How on earth did you compile it? I guess you didn't as you say you're not using VS, just out of interest, what are you using?

Octavient Over a year ago

I don't really know how to use Visual Studio the "right" way. I just use it to edit code, and I run the web site on a local IIS implementation (so I don't use the Build/Rebuild/Debug tools). So, I guess IIS compiles it, right...?

Moby's Stunt Double Over a year ago

Wow, sounds like you're flying by the seat of your pants! You might want to look into VS Express and the publish features of a project. You could save yourself design time headaches such as this by compiling your website in a dev environment. Good luck!

Moby's Stunt Double · Accepted Answer · 2013-04-04 17:53:41Z

0

so I know the requisite DLLs are present and correctly configured.

They may be bin deployed to that project. Have you tried setting CopyLocal to true in the properties of the reference in VS and redeploying?

answered Apr 4, 2013 at 17:53

Moby's Stunt Double

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GeoffreyG · Accepted Answer · 2025-09-11 12:53:42Z

I had this exact same problem for an older ASP.NET Framework site, to which I had recently updated the VS "Solution" (.sln) file to Visual Studio 2022. Per the answers above, I tried adding the System.Web.Extensions assembly tag in my Web.Config file, both manually and using the VS References dialog, WITHOUT success.

After more searching and playing around with things, the fix ended up being a change to the "Target Framework" setting from 4.8.1 to 4.8 and then back to 4.8.1 in the "Property Pages" for the site. Making this change added the following compilation tag (with the targetFramework attribute set to 4.8.1) to my Web.Config file:

<system.web>
  ...
  <compilation targetFramework="4.8.1"/>
</system.web>

And when I did this, I did NOT need the reference to the System.Web.Extensions assembly in my Web.Config file. Just adding the <compilation targetFramework="4.8.1"/> tag alone fixed the compile errors for the "using" statements to the System.Web.Script.Serialization namespace and the compile errors for my JavaScriptSerializer variables.

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