Public Class SomeType1
End Class
Public Class SomeType2
End Class

Dim readOnlyKeyedCollection1 As ReadOnlyKeyedCollection(Of SomeType1, SomeType2)

Dim key As TKey
Dim returnValue As SomeType2
returnValue = readOnlyKeyedCollection1.Item(key)

Public Overridable Overloads ReadOnly Property Item( _
		ByVal key As TKey _
) As TValue

public virtual TValue this[
		TKey key
] {get;}

public:
property virtual TValue default[TKey] {
		TValue get(TKey key);
}

public TValue get_Item(
		TKey key
);

JScript does not support Generics.