How to add `System.Web.Extensions` assembly to .net core project in vscode

Question

I have installed c# support for vscode(version is 1.15.0) and created a HelloWorld project via dotnet new console.

Now in Program.cs

Answer 1

Here I just want to know how to add assembly.

In general, you would have nodes like this in your .csproj:

However, since you are using .NET Core, you cannot reference assemblies that are targeted to the full .NET Framework. In this case, System.Web.Extensions is one of those, so you cannot use it in your .NET Core project.