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CHAPTER 16 Scripting CSS


Scripting CSS

Cascading Style Sheets (CSS) is a standard for specifying the visual presentation of HTML documents. CSS is intended for use by graphic designers: it allows a designer to precisely specify fonts, colors, margins, indentation, borders, and even the position of document elements. But CSS is also of interest to client-side JavaScript programmers because CSS styles can be scripted. Scripted CSS enables a variety of interesting visual effects: you can create animated transitions where document content “slides in” from the right, for example, or create an expanding and collapsing outline list in which the user can control the amount of information that is displayed. When first introduced, scripted visual effects like these were revolutionary. The JavaScript and CSS techniques that produced them were loosely referred to as Dynamic HTML or DHTML, a term that has since fallen out of favor.

CSS is a complex standard that, at the time of this writing, is undergoing active development. CSS is a book-length topic of its own and complete coverage is well beyond the scope of this book.1 In order to understand CSS scripting, however, it is necessary to be familiar with CSS basics and with the most commonly scripted styles, so this chapter begins with a concise overview of CSS, followed by an explanation of key styles that are most amenable to scripting. After these two introductory sections, the chapter moves on to explain how to script CSS. §16.3 explains the most common and important technique: altering the styles that apply to individual document elements using the HTML style attribute. Although an element’s style attribute can be used to set styles, it is not useful for querying an element’s style. §16.4 explains how to query the computed style of any element. §16.5 explains how to alter many styles at once by altering the style attribute of an element. It is also possible, though less common, to script stylesheets directly, and §16.6 shows how to enable and disable stylesheets, alter the rules of existing stylesheets, and add new stylesheets.

1. But see CSS: The Definitive Guide by Eric Meyer (O’Reilly), for example.

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