What is the best way to check if an object is an array or not in Javascript?

Question

Say I have a function like so:

function foo(bar) {
    if (bar > 1) {
       return [1,2,3];
    } else {
       return 1;
    }
}

And s

Answer 1

if(foo(1) instanceof Array)
    // You have an Array
else
    // You don't

Update: I have to respond to the comments made below, because people are still claiming that this won't work without trying it for themselves...

For some other objects this technique does not work (e.g. "" instanceof String == false), but this works for Array. I tested it in IE6, IE8, FF, Chrome and Safari. Try it and see for yourself before commenting below.