Beginning JavaScript with DOM Scripting and Ajax, 2nd Edition

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Chapter 6 ■ Common Uses of JavaScript: Images and Windows For now, here are some things to remember about images and JavaScript: • You can do a lot of preloading with the image objects, but it is not a bulletproof approach. Browser cache settings, broken image links, and proxy servers might mess with your preload script. There are libraries that can help with the preload process. PreloadJS, for example, can help you preload images, sound, and other JavaScript files. If these scripts fail, the user might get stuck or face a constantly changing progress bar, which is frustrating. • Although you can access the properties of each image directly, it might not be the best approach. Leave the visuals to the CSS, and your scripts will not be changed by others who might not know what is going on. • CSS has come a long way since the days of DHTML, and these days it might be a better approach to help the CSS designer by providing hooks rather than achieving a visual effect purely by scripting—an example being the parent rollover you saw earlier. Windows and JavaScript Spawning new browser windows and altering the current window are common uses for JavaScript. These are also annoying and unsafe practices, because you can never be sure if the visitor of your web page can deal with resized windows or will be notified by her user agent when there is a new window. Think of screen-reader users listening to your site or text-browser users. Windows have been used for unsolicited advertising (pop-up windows) and executing code in hidden windows for data-retrieval purposes (phishing) in the past, which is why browser vendors and third-party software providers have come up with a lot of software and browser settings to stop this kind of abuse. Mozilla Firefox users, for example, can choose whether they want pop-up windows and what properties of the window can be changed by JavaScript, as shown in Figure 6-11. Figure 6-11. The advanced JavaScript settings in Mozilla Firefox 174 www.it-ebooks.info
Chapter 6 ■ Common Uses of JavaScript: Images and Windows Other browsers like Microsoft Internet Explorer 7 or Opera 8 disallow hiding the location bar in new windows and can impose size and position constraints on new windows. ■ ■Note This is a point of agreement between different browser manufacturers that want to stop security vulnerabilities. Opening a new window without a visible location bar can allow a malicious attacker to open a pop-up on a third-party site via Cross-Site Scripting (XSS), make it appear as if the window belonged to the site, and ask users to enter information. More about XSS can be found on Wikipedia: http://en.wikipedia.org/wiki/Cross-site_scripting. This is all great news for web surfers, because they can stop unwanted advertising and are less likely to be fooled into giving away their data to the wrong people. It is not such great news for you, because it means that when you want to use windows extensively in JavaScript, you have to test a lot of different scenarios. Such considerations aside, you can still do a lot with windows and JavaScript. Every JavaScript-capable browser provides you with an object called window, whose properties are listed in the next section, as well as some examples on how to use them. Window Properties Following is a list of properties for the window object: ■ ■Note This partial list does not show all the window properties available. If a given property is not supported by a certain browser, I will note that where the property is discussed. • closed: Boolean that indicates whether or not the window was closed (read-only) • defaultStatus: The default status message in the status bar (not supported by Safari) • innerHeight: The height of the document part of the window • innerWidth: The width of the document part of the window • outerHeight: The height of the whole window • outerWidth: The width of the whole window • pageXOffset: Current horizontal start position of the document inside the window (read-only) • pageYOffset: Current vertical start position of the document inside the window (read-only) • status: The text content of the status bar • name: The name of the window • toolbar: Property that returns an object with a visible property of true when the window has a toolbar (read-only) www.it-ebooks.info 175
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Contents at a Glance About the Auth
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Chapter 1 Getting Started with Java
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Chapter 1 ■ Getting Started with
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Shortening Your Scripts via InnerHT
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DOMhelp: Your Own Helper Library Ch
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Chapter 5 Presentation and Behavior
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Chapter 8 Back-End Interaction with
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Replacing XML with JSON Chapter 8
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Summary Chapter 8 ■ Back-End Inte
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Chapter 9 ■ Data Validation Techn
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Chapter 10 Modern JavaScript Case S
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Chapter 10 ■ Modern JavaScript Ca
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APPENDIX A ■ Debugging JavaScript
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Index • A Anonymous function, 67
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■ Index • F Flash of unstyled c
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■ Index initialization method, 17
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Beginning JavaScript with DOM Scrip
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For Dad. Thanks for Saturdays full
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■ Contents The Composite Data Typ
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■ Contents Slide Shows 160 Summar
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■ Contents ■■Chapter 10: Mode
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About the Authors Russ Ferguson is
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Acknowledgments I want to thank eve
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