Beginning JavaScript with DOM Scripting and Ajax, 2nd Edition

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Chapter 10 ■ Modern JavaScript Case Study: A Dynamic Gallery badge.js (continued) show : function(e) { var t = DOMhelp.getTarget(e); if(t.nodeName.toLowerCase() != 'a') { t = t.parentNode; } var y = 0; if(self.pageYOffset) { y = self.pageYOffset; } else if (document.documentElement && document.documentElement.scrollTop) { y = document.documentElement.scrollTop; } else if(document.body) { y = document.body.scrollTop; } badge.container.style.top = y + 'px'; badge.container.style.left = 0 + 'px'; In the show method, you once again retrieve the event target and test that it is a link. You then position the large image container on the screen. Because you don’t know where in the document the badge will be, the safest method to show the image is to read out the scroll position of the document. To achieve this, you need to do a bit of object detection for different browsers. ■ ■Note The current vertical scrolling position is a property of the window object called pageYOffset. This is supported in all browsers except Internet Explorer (IE) before version 9. If no HTML DOCTYPE is specified in the document, the scrollTop property is found in the body element of the document object in IE, Firefox Opera, Chrome, and Safari. You test for all these eventualities and position the image container accordingly by setting the left and top properties of its style attribute collection. This way, you can always be sure that the large image will be visible in the user’s browser window. badge.js (continued) var source = t.getAttribute('href'); var newImg = document.createElement('img'); badge.deletePic(); newImg.setAttribute('src', source); badge.container.appendChild(newImg); DOMhelp.addEvent(badge.container, 'click', badge.deletePic, false); DOMhelp.cancelClick(e); }, You read the href attribute of the link and create a new IMG element. You remove any large image that might already be shown by calling the deletePic() method and set the new image’s src attribute to the href of the link. You add the new image as a child node to the image container, apply an event handler that calls deletePic() when the user clicks the image, and stop the link from being followed by calling cancelClick(). 318 www.it-ebooks.info
Chapter 10 ■ Modern JavaScript Case Study: A Dynamic Gallery badge.js (continued) deletePic : function() { badge.container.innerHTML = ' '; } } DOMhelp.addEvent(window, 'load', badge.init, false); All the deletePic method needs to do is to set the innerHTML property of the container element to an empty string, thus removing the large image. Summary In this chapter, you learned how to enhance already existing HTML structures or dynamic server-side scripts for thumbnail galleries with JavaScript either to become dynamic or to appear more dynamic by not loading the whole document when the user chooses another image or thumbnail subset. Galleries are always fun to create, and coming up with new and flashier solutions for them is also enjoyable. I hope that by learning some of the tricks presented in this chapter you feel confident to play around with them and come up with your own gallery ideas. www.it-ebooks.info 319
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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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Generating a Random Number Chapter
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Chapter 3 From DHTML to DOM Scripti
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Chapter 3 ■ From DHTML to DOM Scr
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Variable and Function Scope Chapter
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Changing Attributes of Elements Cha
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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 6 Common Uses of JavaScript
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Chapter 6 ■ Common Uses of JavaSc
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Rollover Effects on Parent Elements
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Embedded Slide Shows Chapter 6 ■
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User Feedback Methods The user feed
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Chapter 8 Back-End Interaction with
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Chapter 8 ■ Back-End Interaction
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Replacing XML with JSON Chapter 8
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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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