js关闭父窗口时关闭子窗口

var sonid = window.open ("
+ url2 + ", newwindow, height=108, width=200, top="
+ top + ",left=" + left
+ ", toolbar=no, menubar=no, scrollbars=no, resizable=no,location=no, "
+ "status=no,titlebar=no,z-look=1,depended=yes,alwaysRaised=yes)

window.attachEvent("onunload", closeSonwin);
function closeSonwin()
{
sonid.close();
}