arrays are not objects?

I'm trying to port a deepEqual function to compare two objects and I encountered this problem. In Espruino:

>var a = [1,2]
=[ 1, 2 ]
>a instanceof Object
=false

in Chrome:

var a = [1,2]
undefined
a instanceof Object
true

Is there already a deepEqual function for Espruino? I want it to compare the output of test code...