For applications that have multiple windows launched, it is especially important to understand the basics of communicating between windows. Normally, we access the methods and properties of the primary window using the object instance named simply window, or we even omit the reference. However, if we want to access another window we need to use the name of that window. For example, given a window named “mywindow,” we would write content to it using mywindow.document.write. The key to communication between windows is knowing the name of the window and then using that in place of the generic object reference window. Of course, there is the important question of how you reference the main window from a created window? The primary way is using the window.opener property that references the Window object that created the current window. The simple example here shows how one window creates another and each is capable of setting the background color of the other.