JavaScript Bible, Gold Edition part 29 ppsx

isMultiLine NN2 NN3 NN4 NN6 IE3/J1 IE3/J2 IE4 IE5 IE5.5 The isMultiLineproperty returns a Boolean value that reveals whether the ele-ment object is capable of occupying or displaying mor

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The isDisabledproperty returns a Boolean value that indicates whether a par-ticular element object is set to be disabled (see the preceding discussion of the disabledproperty) This property is helpful; if a parent element’s disabled prop-erty is set to true, then a nested element’s disabledproperty likely is set to its default value of false But because its parent is disabled, the isDisabledproperty

of the nested element returns true In other words, the isDisabledproperty returns the actual disabled status of an element regardless of its disabledproperty Example on the CD-ROM

Related Item:disabledproperty

isMultiLine

NN2 NN3 NN4 NN6 IE3/J1 IE3/J2 IE4 IE5 IE5.5

The isMultiLineproperty returns a Boolean value that reveals whether the ele-ment object is capable of occupying or displaying more than one line of text Importantly, this value does not reveal whether the element actually occupies mul-tiple lines; rather, it indicates the potential of doing so For example, a text INPUT element cannot wrap to multiple lines, so its isMultiLineproperty is false However, a BUTTON element can display multiple lines of text for its label, so it reports truefor the isMultiLineproperty

Example on the CD-ROM

isTextEdit

The isTextEditproperty reveals whether an object can have an IE/Windows TextRangeobject created with its content (See the TextRangeobject in Chapter 19.) You can create TextRangeobjects only from a limited selection of objects in IE4+ for Windows: BODY, BUTTON, certain form elements (text, password, hidden,

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elementObject.isTextEdit

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button, reset, and submit types), and TEXTAREA This property always returns

falsein IE5/Mac

Related Items:createRange()method; TextRangeobject (Chapter 19)

lang

The langproperty governs the written language system used to render an

element’s text content when overriding the default browser’s language system

The default value for this property is an empty string unless the corresponding

LANGattribute is assigned a value in the element’s tag Modifying the property

value by script control does not appear to have any effect in the current browser

implementations

language

IE4+’s architecture allows for multiple scripting engines to work with the

browser Two engines are included with the basic Windows version browser: JScript

(compatible with JavaScript) and Visual Basic Scripting Edition (VBScript) The

default scripting engine is JScript But if you wish to use VBScript or some other

scripting language in statements that are embedded within event handler attributes

of a tag, you can specifically direct the browser to apply the desired scripting

engine to those script statements by way of the LANGUAGEattribute of the tag The

languageproperty provides scripted access to that property Unless you intend to

modify the event handler HTML code and replace it with a statement in VBScript

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elementObject.language

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(or any other non-JScript-compatible language installed with your browser), you do not need to modify this property (or read it, for that matter)

Valid values include JScript, javascript, vbscript, and vbs Third-party scripting engines have their own identifier for use with this value Because the LANGUAGEattribute is also used in the <SCRIPT>tag, Internet Explorer 5 observes LANGUAGE=”XML”as well

Related Item: SCRIPT element object.

lastChild

(See firstchild)

length

NN2 NN3 NN4 NN6 IE3/J1 IE3/J2 IE4 IE5 IE5.5 Compatibility ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓

The lengthproperty returns the number of items in an array or collection of objects Its most common application is as a boundary condition in a forloop While arrays and collections commonly use integer values as index values (always starting with zero), the lengthvalue is the actual number of items in the group Therefore, to iterate through all items of the group, the condition expression should include a less-than (<) symbol rather than a less-than-or-equal (<=) symbol, as in the following:

for (var i = 0; i < someArray.length; i++) { }

For decrementing through an array (in other words, starting from the last item in the array and working toward the first), the initial expression must initialize the counting variable as the length minus one:

for (var i = someArray.length - 1; i >= 0; i ) { }

For most arrays and collections, the lengthproperty is read-only and governed solely by the number of items in the group But in more recent versions of the browsers, you can assign values to some object arrays (areas, options, and the SELECT object) to create placeholders for data assignments See discussions of the AREA, SELECT, and OPTION element objects for details A plain JavaScript array can also have its lengthproperty value modified by script to either trim items from the end of the array or reserve space for additional assignments See Chapter 37 for more about the Arrayobject

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elementObjectCollection.length

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Related Items: AREA, SELECT, OPTION, and Arrayobjects

localName

namespaceURI

prefix

NN2 NN3 NN4 NN6 IE3/J1 IE3/J2 IE4 IE5 IE5.5 Compatibility ✓

The three properties, localName, namespaceURI, and prefix, apply to any

node in an XML document that associates a Namespace URI with an XML tag

Although NN6 exposes all three properties for all element (and node) objects, the

properties do not return the desired values Future versions of NN6 should remedy

the situation In the meantime, this description provides a preview of what values

these three properties will represent

Consider the following XML content:

<bk:title>To Kill a Mockingbird</bk:title>

</x>

The element whose tag is <bk:title>is associated with the Namespace URI

defined for the block, and the element’s namespaceURIproperty would return the

string http://bigbooks.org/schema The tag name consists of a prefix (before

the colon) and the local name (after the colon) In the above example, the prefix

property for the element defined by the <bk:title>tag would be bk, while the

localNameproperty would return title The localName property of any node

returns the same value as its nodeNameproperty value, such as #textfor a text

node

For more information about XML Namespaces, visit http://www.w3.org/TR/

REC-xml-names

Related Items:scopeName, tagUrnproperties

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elementObject.localName

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previousSibling

A sibling element is one that is at the same nested level as another element For

example, the following P element has two child nodes (the EM and SPAN elements) Those two child nodes are siblings of each other

MegaCorp is the source of the hottest gizmos.

Sibling order is determined solely by the source code order of the elements Therefore, in the previous example, the EM element has no previousSibling property Meanwhile, the SPAN element has no nextSiblingproperty (meaning that these properties return null) These properties provide another way to iterate through all elements at the same level

Related Items:firstChild, lastChild, childNodesproperties;

hasChildNodes(), insertAdjacentElement()methods

nodeName

For HTML and XML elements, the name of a node is the same as the tag name The nodeNameproperty is provided for the sake of consistency with the node archi-tecture specified by the formal W3C DOM standard The value, just like the tagName property, is an all-uppercase string of the tag name (even if the HTML source code

is written with lowercase tags)

Some nodes, such as the text content of an element, do not have a tag The nodeNameproperty for such a node is a special value: #text Another kind of node

is an attribute of an element For an attribute, the nodeNameis the name of the attribute See Chapter 14 for more about Nodeobject properties

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elementObject.nodeName

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Related Item:tagNameproperty

nodeType

The W3C DOM specification identifies a series of constant values that denote

cat-egories of nodes Not all of these values are implemented in the W3C DOM-capable

browsers, although NN6 includes more than the two supplied by IE5 Table 15-4 lists

the nodeTypevalues implemented in recent browsers

Table 15-4 nodeType Property Values

The nodeTypevalue is automatically assigned to an element, whether the

ele-ment exists in the docuele-ment’s HTML source code or it is generated on the fly via a

script For example, if you create a new element through any of the ways available

by script (for example, by assigning a string encased in HTML tags to the innerHTML

property or by explicitly invoking the document.createElement()method), the

new element assumes a nodeTypeof 1

NN6 goes one step further in supporting the W3C DOM specification by

imple-menting a set of Nodeobject property constants for each of the nodeTypevalues

Table 15-5 lists the entire set as defined in the DOM Level 2 specification (not all of

which are implemented in NN6) Substituting these constants for nodeTypeintegers

can improve readability of a script For example, instead of

if (myElem.nodeType == 1) { }

it is much easier to see what’s going on with

if (myElem.nodeType == Node.ELEMENT_NODE) { }

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elementObject.nodeType

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Table 15-5 W3C DOM nodeType Constants

Node.PROCESSING_INSTRUCTION_NODE 7

Related Item:nodeNameproperty

nodeValue

Of the node types implemented in the W3C DOM-capable browsers, only the text and attribute types have readable values An element’s node value returns a null value

For a text node, the nodeValueproperty consists of the actual text for that node Such a node cannot contain any further nested elements, so the nodeValueproperty offers another way of reading and modifying what Internet Explorer implements as an element’s innerTextproperty

For an attribute node, the nodeValueproperty consists of the value assigned to that attribute According to the W3C DOM standard, attribute values should be

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elementObject.nodeValue

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reflected as strings IE5/Windows, however, returns values of type Numberwhen the

value is all numeric characters Even if you assign a string version of a number to

such a nodeValueproperty, it is converted to a Numbertype internally NN6 and

IE5/Mac return nodeValuevalues as strings in all cases (and convert numeric

assignments to strings)

Related Items:attributes, innerText, nodeTypeproperties

offsetHeight

offsetWidth

It is nearly impossible to reconcile the actual behavior of these properties with

the descriptions provided by Microsoft for Internet Explorer The genuine

complex-ity comes when an element has one or more of the following style features

attached: borders, margins, and padding The property values, especially

offsetWidth, are heavily influenced by the heightand widthattributes assigned

to an element’s style sheet rule The permutations of elements and their styles plus

the vastly roving range of resulting values make it difficult to recommend the

offsetHeightand offsetWidthproperties unless you manage to find the magic

combination that works for your page layout Differences abound in these

proper-ties’ treatment across operating system versions of IE

One advantage that offsetHeightand offsetWidthhave over clientHeight

and clientWidthis that the offset properties have values even when you do not

set dimensions for the element in the HTML tag attributes That’s because these

values are set in relation to the element’s parent element — most often the BODY

element

Be aware that for a normal element whose height and width are not specified,

the offsetHeightis determined by the actual height of the content after all text

flows But the offsetWidthalways extends the full width (plus or minus borders,

margins, and padding) of the containing element Therefore, the offsetWidth

property does not reveal the rendered width of text content that is narrower than

the full parent element width (Through IE5, no property reveals this information.)

To find out the actual width of text within a full-width, block-level element, wrap the

text within an inline element (such as a SPAN) and inspect the offsetWidth

prop-erty of the SPAN

Although the offsetHeightand offsetWidthproperties are not part of the

W3C DOM specification, Netscape has implemented these properties in NN6

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elementObject.offsetHeight

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because they are convenient for some scriptable Dynamic HTML tasks Through these two properties, a script can read the height and width of any block-level or inline element As with IE, the NN6 offsetWidthof a text-oriented block-level ele-ment is the width of the eleele-ment’s container For example, a P eleele-ment consisting of only a few words may report an offsetWidthof many hundreds of pixels because the paragraph’s block extends the full width of the BODY element that represents the containing parent of the P element

Related Items:clientHeight, clientWidthproperties

offsetLeft

offsetTop

The offsetLeftand offsetTopproperties can suffer from the same version vagaries that afflict offsetHeightand offsetWidthproperties when borders, margins, and padding are associated with an element However, the offsetLeft and offsetTopproperties are valuable in providing pixel coordinates of an element within the positioning context of the parent element — even when the elements are not positioned explicitly

The offsetLeft and offsetTop properties for positioned elements in IE/Macintosh do not return the same values as the style.left and style.top properties of the same element See Listing 31-17 for an example of how to cor-rect these discrepancies without having to hard-wire the precise pixel differences

in your code

The element used as a coordinate context for these properties is whatever ele-ment the offsetParentproperty returns This means that to determine the pre-cise position of any element, you may have to add some code that iterates through the offsetParenthierarchy until that property returns null

Although the offsetLeftand offsetTopproperties are not part of the W3C DOM specification, Netscape has implemented these properties in NN6 because they are convenient for some scriptable Dynamic HTML tasks Through these two proper-ties, a script can read the pixel coordinates of any block-level or inline element Measurements are made relative to the BODY element, but this may change in the future See the discussion later in this chapter about the offsetParentproperty

Note

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elementObject.offsetLeft

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Related Items:clientLeft, clientTop, offsetParentproperties

offsetParent

The offsetParentproperty returns a reference to the object that acts as a

posi-tioning context for the current element Values for the offsetLeftand offsetTop

properties are measured relative to the top-left corner of the offsetParentobject

The returned object is usually, but not always, the next outermost block-level

container For most document elements, the offsetParentobject is the

docu-ment.bodyobject (with exceptions for some elements in some browsers)

Table cells, for example, have different offsetParentelements in different

browsers:

Positioned elements also have different results among browsers In IE, a

first-level positioned element’s offsetParentelement is the BODY; the offsetParent

of a nested positioned element (for example, one absolute-positioned DIV inside

another) is the next outer container (in other words, the positioning context of the

inner element)

The situation for NN6, however, is not as straightforward as it could be The

offsetParentfor any unpositioned element on the page is the BODY element But

the offsetParentproperty for a positioned element (or any element nested inside

a positioned element) returns null Even so, the offsetLeftand offsetTop

properties of a positioned element (and its contents) treat the BODY element as the

positioning context This approach complicates the calculation of the position of an

element inside a positioned element relative to its container Future versions of NN6

will likely bring the behavior of the offsetParentproperty in line with the IE

behavior See Chapter 31 for more details on browser-specific treatment of

position-able elements

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elementObject.offsetParent

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