.NET (Core and Framework)

// javascript code
var t = 123;
window.external.Test(t);
alert(t);

// c# code
public void Test(ref int TT){
TT = 456;// TT is changed, but the javascrpt t value is not change.
}

// javascript code
function MyTestClass(){
    this.A = "123MyTestClass";
}
var t = new MyTestClass();
window.external.Test(t);
alert(t.A);

// c# code
public void Test(object TT){
   object s = TT.GetType().InvokeMember("A", BindingFlags.SetProperty, null, TT, new object[] { "mynewvalue" });
}