What is it?

E4X is a programming language extension that adds native XML support to ECMAScript, which includes ActionScript, DMDScript, JavaScript, and JScript. Its creation was intended to provide an alternative to DOM interfaces that uses a simpler syntax for accessing XML documents. It also offers a new way of making XML visible. The first implementation of E4X was designed by Terry Lucas and John Schneider and appeared in BEA’s Weblogic Workshop 7.0 released in February 2002. BEA’s implementation was based on Rhino and released before the ECMAScript E4X spec was completed in June 2004.

Who is it for?

E4X reuses familiar ECMAScript operators for creating, navigating and manipulating XML, making it possible for anyone who has used ECMAScript to be able to start using XML with little or no additional knowledge. The extensions include native XML data types, XML literals and a small set of new operators useful for common XML operations, such as searching and filtering. E4X applications are smaller and more intuitive to ECMAScript developers than comparable XSLT or DOM applications. They are easier to read, write and maintain requiring less developer time, skill and specialized knowledge. The result is less code complexity, tighter revision cycles and shorter time to market for Internet applications. In addition, E4X is a lighter weight technology, allowing a wide range of mobile applications.

Features

E4X is based on six design principles. These non-normative design principles are used to guide the development of E4X and encourage consistent design decisions. The first principle is Simple. E4X is intended to simplify common programming tasks. The second principle is Consistent. The design of E4X is internally consistent, allowing developers to anticipate its behavior. Third is Familiar. Common operators available for manipulating ECMAScript objects should also be available for manipulating XML data. Developers already familiar with ECMAScript objects should be able to begin using XML objects with few surprises. The fourth is Minimal. E4X defines new operators for manipulating XML that are not currently available for manipulating ECMAScript objects where appropriate. This set of operators is to be kept to a minimum to avoid unnecessary complexity. Fifth is Loose Coupling. E4X operators enable applications to minimize dependencies on external data formats. This means that changes in the containment hierarchy of the data will not require changes to the application. The sixth and final design principle is Complementary. E4X integrates well with other languages designed for manipulating XML, such as XPath, XSLT and XML Query.

Compatibility

E4X is implemented in SpiderMonkey, Gecko’s JavaScript engine, and in Rhino, Mozilla’s other JavaScript engine written in Java instead of C. As Mozilla Firefox is based on Gecko, it can be used to run scripts using E4X. The specification is supported in the 1.5 release or later. Adobe’s ActionScript 3 scripting language fully supports E4X. E4X is available in Flash CS3, Adobe AIR and Adobe Flex as they use ActionScript 3 as a scripting language. E4X is also available in Adobe Acrobat and Adobe Reader versions 8.0 or higher.

Web Hosts that Offer E4X