isWindow: optimize for single window
isWindow: optimize for single window

Closes #194

Endika/interact.js,taye/interact.js,taye/interact.js,mcanthony/interact.js,adamgruber/interact.js,mcanthony/interact.js,marian-r/interact.js,bios21/interact.js,Endika/interact.js,taye/interact.js,marian-r/interact.js,bios21/interact.js,adamgruber/interact.js