Mastering JavaScript Design Patterns

Interacting with the user interface

A great deal of JavaScript in use today is used on the client and is used to interact with elements that are visible on the screen. Interacting with the page flows through a model of the page known as the Document Object Model (DOM).

Every element on the page is represented in the DOM. Whenever a change is made to the page, the DOM is updated. If we add a paragraph to the page, then a paragraph is added to the DOM. Thus, if our JavaScript code is to add a paragraph, checking that it does so is simply a function of checking the DOM.

Unfortunately, this requires that a DOM actually exists and that it is formed in the same way that it is on the actual page. There are a number of approaches to doing testing against ...