var test = new Array();
test["a"] = "aa";
test["b"] = "bb";

for (key in test)
  document.write(key + " ");


document.write("<br>");

function Array_assocCount(){
   var c = 0;
   for (key in this) c++;
   return c;
}

Array.prototype.count = Array_assocCount;

var test = new Array();
test["a"] = "aa";
test["b"] = "bb";

for (key in test)
  document.write(key + " ");