tailieunhanh - JavaScript Bible, Gold Edition part 39

JavaScript Bible, Gold Edition part 39. This book will bring programmers and non-technical professionals, including casual programmers and scripters, painlessly up to speed on all aspects of mastering JavaScript. Key topics include programming fundamentals, JavaScript language elements and how to use them effectively, and how to easily and efficiently add powerful new functionality to HTML documents and Java applets. | 228 Part III Document Objects Reference opens a window. That window is a valid window object even if the window is blank. Therefore after a user loads your page into the browser the window object part of that document is automatically created for your script to access as it pleases. One conceptual trap to avoid is believing that a window object s event handler or custom property assignments outlive the document whose scripts make the assignments. Except for some obvious physical properties of a window each new document that loads into the window starts with a clean slate of window properties and event handlers. Your script s control over an existing already open window s user interface elements varies widely with the browser and browser version for which your application is intended. Before the version 4 browsers the only change you can make to an open window is to the status line at the bottom of the browser window. With IE4 and NN4 however you can control such properties as the size location and with signed scripts in Navigator the presence of chrome elements toolbars and scrollbars for example on the fly. Many of these properties can be changed beyond specific safe limits only if you cryptographically sign the scripts see Chapter 46 and or the user grants permission for your scripts to make those modifications. Window properties are far more flexible on all browsers when your scripts generate a new window with the method You can influence the size toolbar or other view options of a window. Recent browser versions provide even more options for new windows including the position of the window and whether the window should even display a title bar. Again if an option can conceivably be used to deceive a user for example silently hiding one window that monitors activity in another window signed scripts and or user permission are necessary. The window object is also the level at which a script asks the browser to display any of three styles of dialog .