JavaScript Bible, Gold Edition part 52 ppt

In IE5.5 and NN6, the DocumentTypeobject even if one is not explicitly defined in the source code is the first child node of the root document node and is thus a sibling to the HTML elem

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Extra batches

You may design a site that needs more than 20 cookies for a given domain For example, in a shopping site, you never know how many items a customer may load into the shopping cart cookie

Because each named cookie stores plain text, you can create your own text-based data structures to accommodate multiple pieces of information per cookie (But also watch out for a practical limit of 2,000 characters per name/value pair within the 4,000 character maximum for any domain’s combined cookies.) The trick

is determining a delimiter character that won’t be used by any of the data in the cookie In Decision Helper (in Chapter 55), for example, I use a period to separate multiple integers stored in a cookie

With the delimiter character established, you must then write functions that con-catenate these “subcookies” into single cookie strings and extract them on the other side It’s a bit more work, but well worth the effort to have the power of persistent data on the client

Example on the CD

Related Items: String object methods (Chapter 34).

defaultCharset

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

The defaultCharsetproperty reveals the character set used by the browser to render the current document You can find possible values for this property at ftp://ftp.isi.edu/in-notes/iana/assignments/character-sets

Each browser and operating system has its own default character set Values may also be set via a <META>tag The difference between the defaultCharsetand charsetproperties is not clear, especially because both are read/write (although modifying the defaultCharsetproperty has no visual effect on the page)

However, if your scripts temporarily modify the charsetproperty, you can use the defaultCharsetproperty to return to the original character set:

document.charset = document.defaultCharset

Example on the CD

Related Items:charset, characterSetproperties

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document.defaultCharset

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The designModeproperty is applicable only when IE5 technology is being used

as a component in another application More information can be found at http://

msdn.microsoft.com/workshop/browser/default.asp The property controls

whether the browser module is being used for HTML editing Modifying the

prop-erty from within a typical HTML page in the IE5 browser has no effect

doctype

The doctypeproperty comes from the W3C Core DOM and returns a

DocumentTypeobject — a representation of the DTD information for the document

In IE5.5 and NN6, the DocumentTypeobject (even if one is not explicitly defined in

the source code) is the first child node of the root document node (and is thus a

sibling to the HTML element)

As of NN6, only a couple of properties of this still-evolving W3C DOM

specifica-tion are implemented Table 18-2 shows the typical DocumentTypeobject property

list and values for a generic HTML page Future DOM specifications will allow these

properties to be read/write

Table 18-2 DocumentType Object in NN6

Related Items: Node object (Chapter 14).

document.doctype

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Value: HTML or XML element object reference Read-Only

The documentElementproperty returns a reference to the HTML (or XML) ele-ment object that contains all of the content of the current docuele-ment The naming of this property is a bit misleading, because the root document node is not an ele-ment, but its only child node is the HTML (or XML) element for the page At best, you can think of this property as providing scripts with an “element face” to the documentobject and document node associated with the page currently loaded in the browser

Example on the CD

Related Items:ownerDocumentproperty (Chapter 15)

domain

Security restrictions can get in the way of sites that have more than one server

at their domain Because some objects, especially the locationobject, prevent access to properties of other servers displayed in other frames, legitimate access

to those properties are blocked For example, it’s not uncommon for popular sites

to have their usual public access site on a server named something such as www.popular.com If a page on that server includes a front end to a site search engine located at search.popular.com, visitors who use browsers with these security restrictions are denied access

To guard against that eventuality, a script in documents from both servers can instruct the browser to think both servers are the same In the preceding example, you would set the document.domainproperty in both documents to popular.com Without specifically setting the property, the default value includes the server name as well, thus causing a mismatch between host names

Before you start thinking that you can spoof your way into other servers, be aware that you can set the document.domainproperty only to servers with the same domain (following the “two-dot” rule) as the document doing the setting

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document.domain

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Therefore, documents originating only from xxx.popular.comcan set their

document.domainproperties to popular.comserver

Related Items:window.open()method; window.locationobject; security

(Chapter 46)

embeds

Whenever you want to load data that requires a plug-in application to play or

dis-play, you use the <EMBED>tag The document.embedsproperty is merely one way

to determine the number of such tags defined in the document:

var count = document.embeds.length

For controlling those plug-ins in Navigator, you can use the LiveConnect

technol-ogy, described in Chapter 44

Related Items: EMBED element object (Chapter 32).

expando

Value: Boolean Read/Write

Microsoft calls any custom property that is not a native property of the

docu-mentobject an expando property By default, most objects in recent generations of

browsers allow scripts to add new properties of objects as a way to temporarily

store data without explicitly defining global variables For example, if you want to

maintain an independent counter of how often a function is invoked, you can create

a custom property of the documentobject and use it as the storage facility:

document.counter = 0

IE4+ lets you control whether the documentobject is capable of accepting

expandoproperties The default value of the document.expandoproperty is true,

thus allowing custom properties But the potential downside to this

permissive-ness, especially during the page construction phase, is that a misspelled native

property name is gladly accepted by the documentobject You may not be aware of

why the title bar of the browser window doesn’t change when you assign a new

string to the document.Titleproperty (which, in the case-sensitive world of

JavaScript, is distinct from the native document.titleproperty)

document.expando

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Example on the CD

Related Items:prototypeproperty of custom objects (Chapter 41)

fgColor

See alinkColor

fileCreatedDate

fileModifiedDate

fileSize

Value: String, Integer (fileSize) Read-Only

These three IE-specific properties return information about the file that holds the current document Two of the properties (not implemented in IE5/Mac) reveal the dates on which the current document’s file was created and modified For an unmodified file, its creation and modified dates are the same The fileSize property reveals the number of bytes of the file

Date values returned for the first two properties are formatted differently between IE4 and IE5 The former provides a full readout of the day and date; the lat-ter in a format similar to mm/dd/yyyy Note, however, that the values contain only the date and not the time In any case, you can use the values as the parameter to a new Date()constructor function You can then use date calculations for such information as the number of days between the current day and the most recent modification

Not all servers may provide the proper date or size information about a file or in

a format that IE can interpret Test your implementation on the deployment server

to ensure compatibility

Also, be aware that these properties can be read only for a file that is loaded in the browser JavaScript by itself cannot get this information about files that are on the server but not loaded in the browser

IE5.5 exposes a property called fileUpdatedDate, but the property does not return any data This property may be a phantom property left over from a prere-lease version

Example on the CD with Listing 18-4

Related Items:lastModifiedproperty

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document.fileCreatedDate

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As I show in Chapter 23, which is dedicated to the form object, an HTML form

(anything defined inside a <FORM> </FORM>tag pair) is a JavaScript object unto

itself You can create a valid reference to a form according to its name (assigned via

a form’s NAMEattribute) For example, if a document contains the following form

definition

input item definitions

</FORM>

your scripts can refer to the form object by name:

document.phoneData

However, a documentobject also tracks its forms in another way: as an array of

Form objects The first item of a document.formsarray is the form that loaded first

(it was first from the top of the HTML code) If your document defines one form, the

forms property is an array one entry in length; with three separate forms in the

document, the array is three entries long

Use standard array notation to reference a particular form from the

document.formsarray For example, the first form in a document (the “zeroth”

entry of the document.formsarray) is referenced as

document.forms[0]

Any of the form object’s properties or methods are available by appending the

desired property or method name to the reference For example, to retrieve the

value of an input text field named homePhonefrom the second form of a document,

the reference you use is

document.forms[1].homePhone.value

One advantage to using the document.formsproperty for addressing a form

object or element instead of the actual form name is that you may be able to

gener-ate a library of generalizable scripts that know how to cycle through all available

forms in a document and hunt for a form that has some special element and

prop-erty The following script fragment (part of a repeat loop described more fully in

Chapter 39) uses a loop-counting variable (i) to help the script check all forms in a

document:

for (var i = 0; i < document.forms.length; i++) {

if (document.forms[i] ) {

statements

}

document.forms

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One more variation on forms array references lets you substitute the name of a form (as a string) for the formsarray index For example, the form named

phoneDatacan be referenced as document.forms[“phoneData”]

If you use a lot of care in assigning names to objects, you will likely prefer the

document.formNamestyle of referencing forms In this book, you see both indexed array and form name style references The advantage of using name references is that even if you redesign the page and change the order of forms in the document, references to the named forms will still be valid, whereas the index numbers of the forms will have changed See also the discussion in Chapter 23 of the form object and how to pass a form’s data to a function

Example on the CD with Listing 18-5

Related Items:formobject (Chapter 23)

frames

The document.framesproperty is similar to the window.framesproperty, but its association with the documentobject may seem a bit illogical at times The objects contained by the array returned from the property are window objects, which means they are the window objects of any FRAME elements (from a frameset-ting document) or IFRAME elements (from a plain HTML document) defined for the document Distinguishing the window objects from the element objects is impor-tant Window objects have different properties and methods than the FRAME and IFRAME element objects The latter’s properties typically represent the attributes for those element’s tags If a document contains no IFRAME elements, the frames array length is zero

While you can access an individual frame object via the typical array syntax (for example, document.frames[0]), you can also use alternate syntax that Microsoft provides for collections of objects The index number can also be placed inside parentheses, as in

document.frames(0) Moreover, if the frames have values assigned to their NAMEattributes, you can use the name (in string form) as a parameter:

document.frames(“contents”)

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document.frames

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And if the collection of frames has more than one frame with the same name, you

must take special care Using the duplicated name as a parameter forces the

refer-ence to return a collection of frame objects that share that name Or, you can limit

the returned value to a single instance of the duplicate-named frames by specifying

an optional second parameter indicating the index For example, if a document has

two IFRAME elements with the name contents, a script could reference the second

windowobject as

document.frames(“contents”, 1)

For the sake of cross-browser compatibility, my preference for referencing frame

window objects is via the window.framesproperty

Example on the CD

Related Items:window.framesproperty

height

width

The heightand widthproperties of the NN4+ documentobject provide the

pixel dimensions of the content within the current window (or frame) If the

docu-ment’s content is smaller than the size of the browser’s content region, the

dimen-sions returned by these properties include the blank space to the right and/or

bottom edges of the content area of the window But if the content extends beyond

the viewable edges of the content region, the dimensions include the unseen

con-tent as well The corresponding measures in IE4+ are the document.body

scrollHeightand document.body.scrollWidthproperties

Example on the CD

Related Items:document.body.scrollHeight, document.body.scrollWidth

properties

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document.height

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The NN4-specific idsproperty is used in the browser’s alternative, JavaScript-based style sheet syntax Deployment of JavaScript style sheets is exceedingly rare

In some ways, the document.idsproperty behaves similarly to the IE4+ document allproperty, but document.idscannot be used in regular scripts to access ele-ment objects

Related Items:tagsproperty

images

With images treated as first-class objects beginning with NN3 and IE4 (and IE ver-sion 3.01 on the Mac), it’s only natural for a document to maintain an array of all the image tags defined on the page (just as it does for links and anchors) The prime importance of having images as objects is that you can modify their content (the source file associated with the rectangular space of the image) on the fly You can find details about the image object in Chapter 22

Use image array references to pinpoint a specific image for retrieval of any image property or for assigning a new image file to its srcproperty Image arrays begin their index counts with 0: The first image in a document has the reference document.images[0] And, as with any array object, you can find out how many images the array contains by checking the length property For example:

var imageCount = document.images.length Images can also have names, so if you prefer, you can refer to the image object

by its name, as in var imageLoaded = document.imageName.complete or

var imageLoaded = document.images[imageName].complete The document.imagesarray is a useful guide to knowing whether a browser supports swappable images Any browser that treats an IMG element as an object always forms a document.imagesarray in the page If no images are defined in the page, the array is still there, but its length is zero The array’s existence, however, is

document.images

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the clue about image object compatibility Because the document.imagesarray

evaluates to an array object when present, the expression can be used as a

condi-tion expression for branching to statements that involve image swapping:

if (document.images) {

// image swapping or precaching here

}

Earlier browsers that don’t have this property evaluate document.imagesas

undefinedand thus the condition is treated as a falsevalue

Example on the CD

Related Items:Imageobject (Chapter 22)

implementation

The Core W3C DOM defines the document.implementationproperty as an

avenue to let scripts find out what DOM features (that is, modules of the DOM

stan-dard) are implemented for the current environment While the object returned by

the property (a DOMImplementationobject) has no properties, it has a method,

hasFeature(), which lets scripts find out, for example, whether the environment

supports HTML or just XML The first parameter of the hasFeature()method is

the feature in the form of a string The second parameter is a string form of the

version number The method returns a Boolean value

A section of the W3C DOM specification, called “Conformance,” governs the

module names (the standard also allows browser-specific features to be tested via

the hasFeature()method) Module names include strings such as HTML, XML,

MouseEvents, and so on

Version numbering for W3C DOM modules corresponds to the W3C DOM level

Thus, the version for the XML DOM module in DOM Level 2 is known as 2.0 Note

that versions refer to DOM modules and not, for instance, the separate HTML

standard

NN6 reports that it conforms to many modules defined in the W3C DOM Level 2,

as shown in Table 18-3 But the indicated support may be misleading According to

the W3C standard, conformance for a module and version should indicate support

for “all the interfaces for that module and the associated semantics.” In some cases,

however, NN6 has merely reserved placeholders for objects, properties, and

meth-ods that are not yet implemented As a result, it is risky to use the hasFeature()

method as a substitute for object detection in scripts For now, you can trust the

reported conformance only as a coarse indication of feature support

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document.implementation

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