What is the JavaScript equivalent to a C# HashSet?

Question

I have a list of a few thousand integer keys. The only thing I need to do with this list is say whether or not a given value is in the list.

For C# I would use a

Answer 1

Actually JavaScript provides a Set object, fairly simple to use:

var set = new Set();
set.add(1);
set.add(2);

set.has(1)    // true

Unfortunately, it is not compatible with IE9.