How to reference JSON serialization in ClassLibrary?

What library I need to reference to use System.Web.Script.Serialization in Class Library?

System.Web has been already referenced but using System.Web.Script.Serialization; still failed. Target Framework is 4.0. In We开发者_开发问答bApplication project everything is fine.

System.Web.Extensions is the assembly you need to reference.

For future reference, this information can be found on the majority of the MSDN Documentation pages. It is found directly under the Inheritance Hierarchy:

Namespace: System.Web.Script.Serialization
Assembly: System.Web.Extensions (in System.Web.Extensions.dll)

MSDN - JavaScriptSerializer Class