A Document object represents the HTML document that is displayed in that window. The Document object has various properties that refer to other objects which allow access to and modification of document content.
The way that document content is accessed and modified is called the Document Object Model, or DOM. The Objects are organized in a hierarchy. This hierarchical structure applies to the organization of objects in a Web document.
- Window object: Top of the hierarchy. It is the out most element of the object hierarchy.
- Document object: Each HTML document that gets loaded into a window becomes a document object. The document contains the content of the page.
- Form object: Everything enclosed in the <form>…</form> tags sets the form object.
- Form control elements: The form object contains all the elements defined for that object such as text fields, buttons, radio buttons, and check boxes.
Here is a simple hierarchy of few important objects: