JavaScript Bible, Gold Edition part 138. 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. | 1218 Part V Putting JavaScript to Work Because of the interpreted nature of JavaScript the distinction between syntax and runtime errors blurs. But as you work through whatever problem halts a page from loading or a script from running you have to be aware of differences between true errors in language and your errors in logic or evaluation. Error Message Notification As the browsers have evolved through several generations the ways in which script errors are reported to the user and to you as the author have also changed. The biggest changes came in IE4 Windows and . Prior to those versions script errors always displayed some kind of alert dialog box with information about the error. Because these alerts could confuse non-technical users the newer browsers except for IE Mac are much more subtle about the presence of errors. In fact the notification mechanism is so subtle that it is easy to miss the fact that a script error has occurred. Even if you do notice you must then exercise your mouse a bit more to view the details. When a script error occurs in IE4 Windows the statusbar displays a yellow alert icon plus a brief text message indicating that an error has occurred. A syntax error that occurs while the page loads usually signifies that the page has loaded but with errors. A runtime error s message simply indicates that an error occurred. To view details about the error you must double-click the yellow icon in the statusbar. The default appearance of the error message alert dialog box window includes a button named Show Details. Clicking this button expands the window to reveal whatever details the browser is reporting about the error. If you leave the window expanded the next time it opens it will also be expanded. It is a good idea for scripters to also check the box that forces the browser to show the error dialog box whenever an error occurs. This is simply a shortcut to manually double-clicking the statusbar error icon. Netscape console windows For .
