Set a reference using the window.open() method:
var childWin = window.open("www.google.com" <etc.>);
Then treat childWin as a whole other window. For example,
childWin.document.getElementById('searchField')
will give you a reference to an element with ID of "searchField". Etc. Rinse and repeat.
与恶龙缠斗过久,自身亦成为恶龙;凝视深渊过久,深渊将回以凝视…