JavaScript

JavaScript was formalized in the ECMAscript language standard and is primarily used in the form of client-side JavaScript, implemented as part of a Web browser in order to provide enhanced user interfaces and dynamic websites. This enables programmatic access to computational objects within a host environment.

JavaScript is a client side web programming language. JavaScript Enhance the web-page capability and it uses all over the internet world. 

what more it can do ?

• Generate custom Web pages ans dynamically alter the appearance of a web page
• Validate the contents of a form on a Web page
• Communicate with java "applets" ina web page 
• Perform traditional programming language tasks 

The Document Object Model (DOM)

The Document Object Model (DOM) is an application programming interface (API) for HTML as well as XML. The DOM maps out an entire page as a document composed of a hierarchy of nodes. Each part of an HTML or XML page is a derivative of a node.

The Browser Object Model (BOM)

The Internet Explorer 3.0 and Netscape Navigator 3.0 browsers feature a Browser Object Model (BOM) that allows access and manipulation of the browser window. Using the BOM, developers can move the window, change text in the status bar, and perform other actions that do not directly relate to the page content. What makes the BOM truly unique, and often problematic, is that it is the only part of a JavaScript implementation that has no related standard.

JavaScript implementation that has no related standard.