779Chapter 30 .Style Sheet and Style Objects The (Crystaltech web hosting)
Wednesday, December 26th, 2007779Chapter 30 .Style Sheet and Style Objects The last object of this quartet of style-related objects is the style object. This object is the motherlode, where actual style definitions take place. In earlier chap ters, you have seen countless examples of modifying one or more styleproperties of an element. Most typically, this modification is accomplished through the style property of the HTML element. For example, you would set the font color of a SPAN element whose ID is hot as follows: document.all.hot.style.color = red // IE4+ document.getElementById( hot ).style.color = red // IE5+, NN6+ The style object is also a property of a rule/cssRuleobject. Thus, if you need to modify the style of elements affected by an existing style sheet rule, you approach the styleobject through a different reference path, but the styleobject is treated just as it is for elements: document.styleSheets[0].rules[0].style.color = red // IE4+ document.styleSheets[0].cssRules[0].style.color = red // IE5/Mac, NN6+ Many scripters concern themselves solely with the style object, and at that, a style object associated with a particular element object. Rare are instances that require manipulation of styleSheet objects beyond perhaps enabling and disabling them under script control. Therefore, if you are learning about these objects for the first time, pay closest attention to the styleobject details rather than to the other related objects. Imported Style Sheets Style sheets embedded in a document via the STYLE element can import additional style sheets via the @importselector: In this example scenario, the document sees just one styleSheet object. But that object has a style sheet nested inside the style sheet defined by the external file. IE4+ calls one of these imported styles sheets an importobject. An import object has all the properties of any styleSheet object, but its parentStyle property is a reference to the styleSheet that owns the @import rule. In fact, the @import statement does not even appear among the rules collection of the IE styleSheet object. Therefore, to access the first rule of the imported style sheet, the reference is as the following: document.styleSheets[0].imports[0].rules[0] The W3C DOM and NN6 treat import rule objects differently from the IE model. To the W3C DOM, even an at-rule is considered one of the cssRules collection of a styleSheet object. One of the properties of a cssRule object is type, which conveys an integer code value revealing whether the rule is a plain CSS rule or one of several other types, including an import rule. Of course, an imported rule object then has as one of its properties the styleSheet object that, in turn, contains the rules
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