tailieunhanh - DHTML Utopia Modern Web Design Using JavaScript & DOM- P6

DHTML Utopia Modern Web Design Using JavaScript & DOM- P6:In a single decade, the Web has evolved from a simple method of delivering technical documents to an essential part of daily life, making and breaking relationships and fortunes along the way. “Looking something up on the Internet,” by which is almost always meant the Web, is now within reach of almost anyone living in a first-world country, and the idea of conducting conversations and business (and probably orchestras) in your Web browser is no longer foreign, but part of life | Chapter 4 Detecting Browser Features does exist but is equal to 0 zero . This is possible because JavaScript treats zero as meaning false. Testing whether a given item is defined just got a little more complex but only a little . If you are testing for the existence of function functionName or method methodName on an object obj use the function method name without the brackets to do so if functionName . if . Likewise if you re testing for a variable v or for a DOM property prop of an object you can often use the variable or the DOM attribute s property name directly if v . if . But watch out If the variable or property contains numbers or strings as does off setHeight for example then use typeof because a number might be 0 zero and a string might be the empty string both which also evaluate to false if typeof v undefined . if typeof undefined . Sniffing at Work scrollImage Lots of Websites contain photo galleries pages listing thumbnails of photographs that when clicked on display the photos at full size. An interesting enhancement to such a site might be to let the user see the full-size photo without having to click to load it. When the user mouses over the thumbnail that thumbnail could become a viewing area in which a snippet of the full-sized image is shown. This technique is useful if your thumbnails aren t detailed enough to enable users to tell the difference between superficially similar images. It s especially handy if your thumbnails display something like a document rather than a photo. Figure shows the final effect 80 Licensed to siowchen@ Setting Up the Page Figure . The thumbnail display implemented by the scrollImage example. We ll describe what s going on here in a moment. We ll review the code first then see a demonstration before we get to the explanation. Setting Up the Page The HTML file for this technique is straightforward File DOCTYPE HTML PUBLIC - W3C DTD .