[zirak]

The constructor check would unfortunately not work for cross-frame arrays. Each frame has its own global object, with its own Array constructor. So:

    var iframe = document.createElement('frame');
    document.body.appendChild(iframe);

    var value = iframe.contentWindow.Array();
    value.constructor === Array // false
    value instanceof Array // false
    value instanceof iframe.contentWindow.Array // true

Stringifying the constructor works even for cross-frame values:

    value.constructor.toString() === Array.toString() // true

These days though, `Array.isArray` is the right thing to do, available since roughly 2010.