CollectionExtensionsGetOrAddTKey, TValue(IDictionaryTKey, TValue, TKey, FuncTKey, TValue) Method

public static TValue GetOrAdd<TKey, TValue>(
	this IDictionary<TKey, TValue> dictionary,
	TKey key,
	Func<TKey, TValue> valueFactory
)

<ExtensionAttribute>
Public Shared Function GetOrAdd(Of TKey, TValue) ( 
	dictionary As IDictionary(Of TKey, TValue),
	key As TKey,
	valueFactory As Func(Of TKey, TValue)
) As TValue

public:
[ExtensionAttribute]
generic<typename TKey, typename TValue>
static TValue GetOrAdd(
	IDictionary<TKey, TValue>^ dictionary, 
	TKey key, 
	Func<TKey, TValue>^ valueFactory
)

[<ExtensionAttribute>]
static member GetOrAdd : 
        dictionary : IDictionary<'TKey, 'TValue> * 
        key : 'TKey * 
        valueFactory : Func<'TKey, 'TValue> -> 'TValue 

JavaScript does not support generic types or methods.