// create an array of popup window object. This is a global variable
var popups = new Array();
function openPopUp(url,name)
{
var popUp = window.open(url,name,"width=100,height=100");
popups.push(popUp);
}
<body onunload="destroyPopUps()">
function destroyPopUps()
{
if(popups.length == 0) return;
for(i=0; i<popups.length; i++)
{
popups[i].close();
}
}