How to update child window?

I have already opened child window by following code

var myWindow = window.open('','','width=1250,height=1000,resizable=yes,fullscreen=yes');
var doc = myWindow.document;
doc.open();
doc.write(divText);
doc.close();

now I am trying to update the html of that already opened myWindow. How will I be able to do that?