Credit: Mulchaey et al (ST Sci/UMD/NASA)
The Document Object Model (DOM) is that set of
hierarchical
classes and objects and their elements that belong to the
Document part of
a Web page, but can also be extended to include the entire Web structure
from the main Window on down as
depicted here . The names and references used in this DOM are very
similar in Netscape and Internet Explorer for ordinary HTML, but differ
greatly for Dynamic HTML (DHTML). Also, see
here for how this elements can be listed.
The key to successful navigation is understanding how these objects and
elements are referenced. Most can be referenced either by name or
by index, as demonstrated in
this
example.
In a similar manner you can refer to images that appear in
<IMG SRC...> statements either by name or by
document.images[0], document.images[1],
You can not only go down the hierarchy, but up as well. Thus if you are
in an element inside a form, then
this.form.elements[2] refers to the 3rd (sibling) element
of that form.
The value property can be confusing. The rules are:
- for Text and TextArea the "value" is what you type in
- for Radio and Checkboxes, the "value" is what appears in
the 'VALUE=..' part of the element, e.g., VALUE="home".
But to determine if that value is selected you use the
checked property
- the
select has the "value" listed in its list
of "OPTION VALUE=" values. The one that is selected is
its value.
Frames are independently scrollable areas in a window that behave very
much like independent windows.
See
this
for an example of how to
reference and manipulate Frames in HTML.
