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Javascript Certification

ProCert Javascript covers client side scripting.

What is Javascript?

JavaScript is a prototype-based scripting language with a syntax loosely based on C. Like C, it has the concept of reserved keywords, which (being executed from source) means it is almost impossible to extend the language without breakage.

Also like C, the language has no input or output constructs of its own. Where C relies on standard I/O libraries, a JavaScript engine relies on a host program into which it is embedded. There are many such host programs, of which web technologies are the most well known examples. These are examined first.

JavaScript embedded in a web browser connects through interfaces called Document Object Model (DOM) to applications, especially to the server side (web servers) and the client side (web browsers) of web applications. Many web sites use client-side JavaScript technology to create powerful dynamic web applications. It may use unicode and can evaluate regular expressions (introduced in version 1.2 in Netscape Navigator 4 and Internet Explorer 4). JavaScript expressions contained in a string can be evaluated using the eval function.

One major use of web-based JavaScript is to write functions that are embedded in or included from HTML pages and interact with the DOM of the page to perform tasks not possible in static HTML alone, such as opening a new window, checking input values, changing images as the mouse cursor moves over, etc. Unfortunately, the DOM interfaces in various browsers differ and don't always match the W3C DOM standards. Different browsers expose different objects and methods to the script. It is therefore often necessary to write different variants of a JavaScript function for the various browsers, though this situation is improving. Major design methodologies using JavaScript to interact with DOM include DHTML, Ajax, and SPA.

Outside of the Web, JavaScript interpreters are embedded in a number of tools. Adobe Acrobat and Adobe Reader support JavaScript in PDF files. The Mozilla platform, which underlies several common web browsers, uses JavaScript to implement the user interface and transaction logic of its various products. JavaScript interpreters are also embedded in proprietary applications that lack scriptable interfaces. Dashboard Widgets in Apple's Mac OS X v10.4 are implemented using JavaScript. Microsoft's Active Scripting technology supports JavaScript-compatible JScript as an operating system scripting language. JScript .NET is a CLI-compliant language that is similar to JScript, but has further object oriented programming features.

Each of these applications provides its own object model which provides access to the host environment, with the core JavaScript language remaining mostly the same in each application.



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