js window.open

The open() method is used to open a new browser window or find a named window.

//新窗口打开页面 ‘a.htm’ 如果该窗口已经存在，则显示到前台。如果不存在则新打开一个。 
var opendwindow = window.open('', 'windowName',{});
opendwindow.focus();
if(opendwindow.location.href.indexOf('/a.html) == -1 ){
    opendwin.location.href = win_url;
}