global object in a browser, and it can also be treated as the root of the document object model. You can access it as
window.screen or just
screen is a small information object about physical screen dimensions.
window.document or just
document is the main object of the potentially visible (or better yet: rendered) document object model/DOM.
window is the global object, you can reference any properties of it with just the property name – so you do not have to write down
window. – it will be figured out by the runtime.