javascript

Chapter 10: The Document Object Model
In this code, the radio buttons all have a name attribute of “ color ” even though their IDs are different.
The IDs allow the < label > elements to be applied to the radio buttons, and the name attribute assures
that only one of the three values will be sent to the server. These radio buttons can all then be retrieved
using the following line of code:
var radios = document.getElementsByName(“color”);
As with getElementsByTagName() , the getElementsByName() method returns an HTMLCollection .
In this context, however, the namedItem() method always retrieves the first item (since all items have the
same name ).
Special Collections
The document object has several special collections. Each of these collections is an HTMLCollection
object and provides faster access to common parts of the document, as described here:
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document.anchors — Contains all < a > elements with a name attribute in the document.
document.applets — Contains all < applet > elements in the document. This collection is
deprecated, because the < applet > element is no longer recommended for use.
document.forms — Contains all < form > elements in the document. The same as document
.getElementsByTagName( “ form ” ) .
document.images — Contains all < img > elements in the document. The same as document
.getElementsByTagName( “ img ” ) .
document.links — Contains all < a > elements with an href attribute in the document.
These special collections are always available on HTMLDocument objects and, like all HTMLCollection
objects, are constantly updated to match the contents of the current document.
DOM Conformance Detection
Because there are multiple levels as well as multiple parts of the DOM, it became necessary to determine
exactly what parts of the DOM a browser has implemented. The document.implementation property
is an object containing information and functionality tied directly to the browser ’ s implementation of the
DOM. DOM Level 1 specifies only one method on document.implementation , which is
hasFeature() . The hasFeature() method accepts two arguments: the name and version of the DOM
feature to check for. If the browser supports the named feature and version, this method returns true , as
with this example:
var hasXmlDom = document.implementation.hasFeature(“XML”, “1.0”);
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