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152 Part III .Document Objects Reference Table 15-7 (continued) DOMAttrModified mouseout DOMCharacterDataModified mouseover DOMFocusIn mouseup DOMFocusOut reset DOMNodeInserted resize DOMNodeInsertedIntoDocument scroll DOMNodeRemoved select DOMNodeRemovedFromDocument submit DOMSubtreeModified unload Note that the event types specified in the DOM Level 2 are more limited than the wide range of events defined in IE4+. Also, the W3C temporarily tabled the issue of keyboard events until DOM Level 3. Fortunately, Netscape implements keyboard events in a fashion that likely will appear as part of the W3C DOM. The second parameter of the addEventListener()method is a reference to the JavaScript function to be invoked. This is the same form used to assign a function to an event property of an object (for example, objReference.onclick = someFunction), and it should not be a quoted string. This approach also means that you cannot specify parameters in the function call. Therefore, functions that need to reference forms or form control elements must build their own references (with the help of the event object s property that says which object is the event s target). By default, the W3C DOM event model has events bubble upward through the element container hierarchy starting with the target object of the event (for example, the button being clicked). However, if you specify true for the third parameter of the addEventListener() method, event capture is enabled for this particular event type whenever the current object is the event target. This means that any other event type targeted at the current object bubbles upward unless it, too, has an event listener associated with the object and the third parameter is set to true. NN6 does not always set event capture for an element, even when you specify true as the third parameter of addEventListener(). For the most part, you can make do with event bubbling by adding an event listener to a container higher up the element hierarchy. Because event capture is a part of the W3C DOM event model, this feature will likely be implemented in a future version of NN. Using the addEventListener() method requires that the object to which it is attached already exist. Therefore, you most likely will use the method inside an initialization function triggered by the onLoadevent handler for the page. (The document object can use addEventListener()for the load event immediately because the document object exists early in the loading process.) Caution elementObject.addEventListener()
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151Chapter 15 .Generic HTML Element Objects Example (with Listings 15-19a and 15-19b) on the CD-ROM Related Items: readyState property; removeBehavior() method; behaviors (Chapter 48). addEventListener( eventType , listenerFunc, useCapture) removeEventListener( eventType , listenerFunc, useCapture) Returns: Nothing. NN2 NN3 NN4 NN6 IE3/J1 IE3/J2 IE4 IE5 IE5.5 Compatibility The W3C DOM s event mechanism accommodates both event bubbling and trickling (see Chapter 29). While the new mechanism supports the long-standing notion of binding an event to an element by way of HTML attributes (for example, the old onClick event handler), it encourages binding events by registering an event listener with an element. (In browsers that support the W3C event model, other ways of binding events such as event handler attributes are internally converted to registered events.) To tell the DOM that an element should listen for a particular kind of event, use the addEventListener()method on the element object. The method requires three parameters. The first is a string version of the event type for which the element should listen. Event type strings do not include the well-used on prefix of event handlers. Instead, the names consist only of the event and are usually in all lowercase (except for some special system-wide events preceded by DOM). Table 15-7 shows all the events recognized by the W3C DOM specification (although NN6 may not implement them all). Table 15-7 W3C DOM Event Listener Types abort error blur focus change load click mousedown DOMActivate mousemove Continued On the CD-ROM elementObject.addEventListener()
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150 Part III .Document Objects Reference To guarantee that an element gets only one ID assigned to it while the object exists in memory, assign the value via the uniqueIDproperty of that same object not some other object. Once you retrieve the uniqueID property of an object, the property s value stays the same no matter how often you access the property again. In general, you assign the value returned by the uniqueIDproperty to the object s id property for other kinds of processing. (For example, the parameter of a getElementById() method requires the value assigned to the id property of an object.) Example (with Listing 15-18) on the CD-ROM Related Items: id property; getElementById() method. Methods addBehavior( URL ) Returns: Integer ID. NN2 NN3 NN4 NN6 IE3/J1 IE3/J2 IE4 IE5 IE5.5 Compatibility The addBehavior() method imports an external Internet Explorer behavior and attaches it to the current object, thereby extending the properties and/or methods of that object. See Chapter 48 for details on IE behaviors (new in IE5 for Windows). The sole parameter of the addBehavior() method is a URL pointer to the behavior component s code. This component may be in an external file (with an .htc extension), in which case the parameter can be a relative or absolute URL. IE also includes a library of built-in (default) behaviors, whose URLs are in the following format: #default#behaviorName Here, behaviorName is one of the default behaviors (see Chapter 48). If the behavior is imported into the document via the OBJECT tag, the addBehavior() method parameter is the ID of that element in the following format: #objectID When you add a behavior, the loading of the external code occurs asynchronously. This means that even though the method returns a value instantly, the behavior is not necessarily ready to work. Only when the behavior is fully loaded can it respond to events or allow access to its properties and methods. Behaviors loaded from external files observe domain security rules. The behavior component and the HTML page that loads it must come from the same server and domain; they also must load via the same protocol (for example, http://, https://, and file:// are mutually exclusive, mismatched protocols). On the CD-ROM elementObject.addBehavior()
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149Chapter 15 .Generic HTML Element Objects NN2 NN3 NN4 NN6 IE3/J1 IE3/J2 IE4 IE5 IE5.5 Compatibility The W3C standard states that you should use the titleproperty (and TITLE attribute) in an advisory role. The main browsers interpret that role as text assigned to tooltips that pop up momentarily while the cursor rests atop an element. The advantage of having this property available for writing is that your scripts can modify an element s tooltip text in response to other user interaction on the page. A tooltip can provide brief help about the behavior of icons or links on the page. It can also convey a summary of key facts from the destination of a link, thus enabling a visitor to see vital information without having to navigate to the other page. For example, Microsoft s Web authoring documentation online (http:// msdn.microsoft.com) uses the tooltips in listings of scriptable properties to display a list of elements for which the property is available. While this information also appears on the destination of the link for each property, you can see at a glance, for instance, which instance of the two listings for the same property name apply to the object in which you re interested. The browser governs tooltip font and color characteristics, which are not changeable via scripting. As with setting the status bar, I don t recommend using tooltips for conveying mission-critical information to the user. Not all users are patient enough to let the pointer pause for the tooltip to appear. On the other hand, a user may be more likely to notice a tooltip once it appears rather than a status bar message (even though the latter appears instantaneously). Example (with Listing 15-17) on the CD-ROM Related Item: window.status property. uniqueID Value: String Read-Only NN2 NN3 NN4 NN6 IE3/J1 IE3/J2 IE4 IE5 IE5.5 Compatibility You can let the IE5+/Windows browser generate an identifier (id property) for a dynamically generated element on the page with the aid of the uniqueID property. You should use this feature with care because the ID it generates at any given time may differ from the ID generated the next time the element is created in the page. Therefore, you should use the uniqueID property when your scripts require an unknown element to have an id property but the algorithms are not expecting any specific identifier. On the CD-ROM elementObject.uniqueID
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148 Part III .Document Objects Reference Example on the CD-ROM Related Items: nodeName property; getElementsByTagName() method. tagUrn Value: String Read-Only NN2 NN3 NN4 NN6 IE3/J1 IE3/J2 IE4 IE5 IE5.5 Compatibility The tagUrn property is associated primarily with XML that is embedded within a document. When you include XML, you can specify one or more XML Namespaces that define the owner of a custom tag name thus preventing conflicts of identical custom tags from different sources in a document. (See Chapter 33 for more about XML objects.) A Namespace definition can include a Uniform Resource Name (URN) that lets a page link to a destination on the network that further defines such Namespace aspects as a behavior associated with a custom XML element. The XML Namespace is assigned (in IE5+) as an attribute of the tag that surrounds the entire document. After that, the namespace value precedes all custom tags linked to that Namespace: To find out the URN of the namespace owner of an element, you can read the tagUrn property of that element. For the preceding example, the tagURN property returns www.giantco.com/xmllib. For regular HTML elements, the returned value is always null. The corresponding property in the W3C DOM and NN6 is namespaceURI. Example on the CD-ROM Related Item: scopeName property. title Value: String Read/Write On the CD-ROM On the CD-ROM elementObject.title
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147Chapter 15 .Generic HTML Element Objects the browsers treat form elements as focusable elements by default. Nonform elements usually don t receive focus unless you specifically set their tabIndex properties (or TABINDEX tag attributes). If you set the tabIndexproperty of one form element to 1, then that element is first in the tabbing order. Meanwhile, the rest fall into source code tabbing order on successive presses of the Tab key. If you set two elements to, say, 1, then the tabbing proceeds in source code order for those two elements and then onto the rest of the elements in source code order starting with the top of the page. In Internet Explorer, you can remove an element from tabbing order entirely by setting its tabIndex property to -1. Users can still click those elements to make changes to form element settings, but tabbing bypasses the element. Example (with Listing 15-16) on the CD-ROM Related Items: blur(), focus() methods. tagName Value: String Read-Only NN2 NN3 NN4 NN6 IE3/J1 IE3/J2 IE4 IE5 IE5.5 Compatibility The tagName property returns a string of the HTML or (in IE5+ and NN6) XML tag name belonging to the object. All tagNamevalues are returned in all uppercase characters, even if the source code is written in all lowercase or a mixture. This consistency makes it easier to perform string comparisons. For example, you can create a generic function that contains a switch statement to execute actions for some tags and not others. The skeleton of such a function looks like the following: function processObj(objRef) { switch (objRef.tagName) { case TR : [statements to deal with table row object] break case TD : [statements to deal with table cell object] break case COLGROUP : [statements to deal with column group object] break default: [statements to deal with all other object types] } } On the CD-ROM elementObject.tagName
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146 Part III .Document Objects Reference style Value: style object reference Read/Write NN2 NN3 NN4 NN6 IE3/J1 IE3/J2 IE4 IE5 IE5.5 Compatibility The style property is the gateway to an element s style sheet settings. The property s value is a style object whose properties enable you to read and write the style sheet settings for the element. While scripts do not usually manipulate the style object as a whole, it is quite common in a Dynamic HTML page for scripts to get or set multiple properties of the styleobject to effect animation, visibility, and all appearance parameters of the element. Changing properties of the style object may affect the layout of the page. For example, setting the font size of an element to a larger value forces the paragraph to reflow to accommodate the enlarged text. This page reflow is available in IE4+ and NN6. Because NN4 cannot reflow content, severe limitations are placed on changing content after the page loads. You can find significant differences in the breadth of properties of the style object in IE compared with NN. See Chapter 30 for more details on the style object. Example on the CD-ROM Related Items: currentStyle, runtimeStyle properties; style object (Chapter 30). tabIndex Value: Integer Read/Write NN2 NN3 NN4 NN6 IE3/J1 IE3/J2 IE4 IE5 IE5.5 Compatibility The tabIndex property controls where in the tabbing sequence the current object receives focus. This property obviously applies only to elements that can receive focus. IE5+ permits giving focus to more elements than IE4 or NN6; but for all browsers compatible with this property, the primary elements for which you may want to control focus (namely form input elements) are covered. IE4/Mac does not give focus to elements other than those that accept text input. The default value of the tabIndex property is 0(although it is -1in NN6). A value of 0(or -1in NN6) means that elements receive focus in the normal tabbing order on the page, following source code order from the first focusable element. In general, On the CD-ROM elementObject.tabIndex
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145Chapter 15 .Generic HTML Element Objects multiframe environment) vertically, the scrollTopproperty of the bodyobject is whatever the pixel distance is between the top of the object (now out of view) and the first visible row of pixels of the element. But the scrollTopvalue of a table that is in the document remains at zero. These properties are available only to the BODY, BUTTON, CAPTION, DIV, FIELDSET, LEGEND, MARQUEE, SPAN, and TEXTAREA objects in IE4. For IE5+, the properties are available to virtually every element. NN treats scrolling of a BODY element from the point of view of the window. If you want to find out the scrolled offset of the current page in NN4+, use window. scrollX and window.scrollY. Example on the CD-ROM Related Items: clientLeft, clientTop properties; window.scroll() method. sourceIndex Value: Integer Read-Only NN2 NN3 NN4 NN6 IE3/J1 IE3/J2 IE4 IE5 IE5.5 Compatibility The sourceIndex property returns the numeric index (zero-based) of the object within the document.allcollection. This property is useful if a script needs to access an adjacent object on a page. For example, the following function receives an object reference as a parameter and returns a reference to the object that is next in the source code object order: function getNextObject(obj) { return document.all[(obj.sourceIndex + 1)] } Or if you know only the ID of an object and want to retrieve a reference to the next object in source code order, you can use the following version: function getNextObject(objName) { var index = document.all[objName].sourceIndex return document.all[(index + 1)] } Example on the CD-ROM Related Item: item() method. On the CD-ROM On the CD-ROM elementObject.sourceIndex
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144 Part III .Document Objects Reference scrollHeight scrollWidth Value: Integer Read-Only NN2 NN3 NN4 NN6 IE3/J1 IE3/J2 IE4 IE5 IE5.5 Compatibility The scrollHeight and scrollWidthproperties contain the pixel measures of an object, regardless of how much of the object is visible on the page. Therefore, if the browser window displays a vertical scrollbar, and the body extends below the bottom of the viewable space in the window, the scrollHeight takes into account the entire height of the body as if you were to scroll downward and see the entire element. For most elements that don t have their own scrollbars, the scrollHeight and scrollWidthproperties have the same values as the clientHeight and clientWidthproperties. A few compatibility cautions are necessary, however. While these properties are available for virtually every element in IE5+, they are available for only the BODY, BUTTON, CAPTION, DIV, FIELDSET, LEGEND, MARQUEE, and TEXTAREA objects in IE4 for Windows. Moreover, IE for the Macintosh yields the viewable height and width of the BODY element, rather than its true scrolling height and width. The values are accurate, however, for other content elements. Example on the CD-ROM Related Items: clientHeight , clientWidth properties; window.scroll() method. scrollLeft scrollTop Value: Integer Read-Only NN2 NN3 NN4 NN6 IE3/J1 IE3/J2 IE4 IE5 IE5.5 Compatibility If an element is scrollable (in other words, it has its own scrollbars), you can find out how far the element is scrolled in the horizontal and vertical direction via the scrollLeft and scrollTopproperties. These values are pixels. For non-scrollable elements, these values are always zero even if they are contained by elements that are scrollable. For example, if you scroll a browser window (or frame in a On the CD-ROM elementObject.scrollLeft
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143Chapter 15 .Generic HTML Element Objects returns contains all style attributes and the default settings at the time the page loads. This property does not reflect values assigned to elements by style sheets in the document or by scripts. The default values returned by this property differ from the values returned by the currentStyleproperty. The latter includes data about values that are not assigned explicitly by style sheets, yet are influenced by the default behavior of the browser s rendering engine. In contrast, the runtimeStyle property shows unassigned style values as empty or zero. To change a style property setting, access it via the element s style object. Example on the CD-ROM Related Items: currentStyle property; style object (Chapter 30). scopeName Value: String Read-Only NN2 NN3 NN4 NN6 IE3/J1 IE3/J2 IE4 IE5 IE5.5 Compatibility The scopeName property is associated primarily with XML that is embedded within a document. When you include XML, you can specify one or more XML Namespaces that define the owner of a custom tag name, thus aiming toward preventing conflicts of identical custom tags from different sources in a document. (See Chapter 33 for more about XML objects.) The XML Namespace is assigned (in IE5+) as an attribute of the tag that surrounds the entire document: After that, the Namespace value precedes all custom tags linked to that Namespace: To find out the Namespace owner of an element, you can read the scopeName property of that element. For the preceding example, the scopeNamereturns Fred. For regular HTML elements, the returned value is always HTML. The scopeName property is available only in Win32 and UNIX flavors of IE5. The comparable property in the W3C DOM is localName. Example on the CD-ROM Related Item: tagUrn property. On the CD-ROM On the CD-ROM elementObject.scopeName
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