Check if array is empty

Hi,

how can i check if an array is initionalized like this

var arrayEmp=[];

but is empty

something like this but this doesnt work

if(arrayEmp="")
{
alert(1);
}

if(A && A.length==0)
or if you have other objects that A may be:
if(A && A.constructor==Array && A.length==0)