JavaScript uses a hierarchical structure that applies to the objects in a document. There are some objects that show the relationship of one object to another using the language.

Window object :

This is the topmost object in the hierarchy. It represent the content area of browser window that consists of HTML documents. Each frame is also a window that has some actions inside it.

Document object :

This object gets loaded in a window and consists of objects of different kind in the model. It consists of the content that will be written in the script.

Form object :

Form objects are used for more interaction with the users. It represents the form elements inside <FORM>...</FORM> tag.