on close pop-up

[NDK]

Hi, i have a question

at the moment, this is my code

function executeWFAction2 (moveType, nodeId, target) {
makeUserOwner(nodeId,"current");
var url = "/wfaction/"+moveType+"?id="+nodeId;

var options = "menubar=no,scrollbars=no,statusbar=no";
var width = 320;
var height = 350;
var haut=(screen.height-height)/2;
var Gauche=(screen.width-width)/2;
popup=window.open(url,"nom","top="+haut+",left="+Gauche+",width="+width+",height="+height+","+options);
makeUserOwner(nodeId,"empty");
}

the code works BUT i want that the last line, makeUserOwner(), only start when the pop-up has been closed...

How can i call an "onClose" method for a pop-up?