Window is the main JavaScript object root, aka the Global object in a browser, also can be treated as the root of the document object model. This window object has the majority of the properties like length, inner Width, inner Height, name, if it has been closed, its parents, and more. You can access it as “window”.

Screen is a small information object about physical screen dimensions. You can access it as “screen” or “window.screen.

Document is the main object of the potentially visible document object model/DOM. The document object is your html, aspx, php, or other document that will be loaded into the browser. The document actually gets loaded inside the window object and has properties available to it like title, URL, cookie, etc. You can access it as “document” or “window.document.

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When you type an URL(Uniform Resource Locator)and hit enter , a HTTP request is sent to the server and server responds with an HTTP response ,that response contains requested URL’s homepage.

In detail ,what happens is, when you type an URL in your browser, it goes to DNS which takes the URL and gives out the IP address and uniquely identifies the server which has the requested HTML page. Once the match is found IP address is send back to the browser. Now the browser has the IP address it is sent to ISP and it requests matched server to send the html page which will be displayed on the browser.

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