Two Types of Containment
If you have worked with JavaScript and the scriptable document object
models inside Navigator and Internet Explorer, you are aware that
scriptable document objects have a containment hierarchy of their
own—an object
containment
hierarchy. The window
object, which
represents the content area of a browser window or frame, is at the
top of the hierarchy. The window
object contains
objects such as the history
,
location
, and document
objects.
The document
object contains objects such as
images and forms, and, among the most deeply nested objects, the
form
object contains form elements, such as text
fields and radio buttons.
Document object containment is
important in JavaScript because the hierarchy defines how you refer
to objects and their methods and properties in your scripts.
References usually start with the outermost element and work their
way inward, using the JavaScript dot syntax to delimit each object.
For example, here’s how to reference the content of a text
field (the value
property) named
zipCode
inside a form named
userInfo
:
window.document.userInfo.zipCode.value
Unlike most object-oriented worlds (such as Java), the object-based world of scriptable browsers does not strictly adhere to the notion of parents and children. In fact, except for the relationship between a frameset document and the frames it creates, the word “parent” is not part of the object containment vocabulary. Document objects do not inherit properties or methods of objects ...
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