When you do a typeof on an array in Flash, it gives you object. So how do you go about finding out if it is an array? There are a few ways to do it, one is you can try finding out the length of it. Any array should have a length of at least 0. Another way is you can try testing for one of Array's method existence, like so:

if (typeof (myarray.splice.toString()) == "String") trace("it's an array");