Navigator 2.0, Internet Explorer 3.0
The close() method closes the top-level browser window specified by window. A window can close itself by calling self.close() or simply close(). In Navigator, if window is the only open window, then close() closes it and Navigator exits.
In Navigator 3.0, only windows that are opened by JavaScript can be closed by JavaScript. This prevents malicious scripts from causing the user's browser to exit.
In Navigator 2.0 and 3.0, there is no meaningful way to close a frame within a window. Thus, the close() method should only be invoked for Window objects that represent top-level browser windows, not those that represent frames.