Wonder if this is something that should work. I think it should:

    try {
         throw new Error('awesome');
    } catch (ex) {
        if (ex instanceof Error) {
            console.log(ex.foo);  // compiles. Should be error
        }
    }

The reason is that ex is still of type any. I suspect its in the spec that instanceof guard will not work on type any (I haven't checked).

Would be great if we could have this though.