You do a whole lot of searching there.

Writing a.b is the same as writing a["b"]. So you can create an object and store things in it by saying:

a["b"] = 42;

Equally well you can text if there is already a value there thus:

if (a["b"] == null) a["b"] = 10;

And where I’ve used the constant "b", you can use a variable.

function ext(id)
{
return a[id] != null;
}

And it should make your code smaller and faster!