In 2002, a group of companies led by BEA Systems proposed an extension to ECMAScript to add native XML support to the language. In June 2004, ECMAScript for XML (E4X) was released as ECMA-357, which was revised in December 2005. E4X is not its own language; rather, it is an optional extension to the ECMAScript language. As such, E4X introduces new syntax for dealing with XML, as well as for XML-specific objects.
Though browser adoption has been slow, Firefox versions 1.5 and later support almost the entire E4X standard. This chapter focuses on the Firefox implementation.
As an extension to ECMAScript, E4X introduces the following new global types:
XML — Any single part of an XML structure
XMLList — A collection of XML objects
Namespace — Mapping between a namespace prefix and a namespace URI
QName — A qualified name made up of a local name and a namespace URI
Using these four types, E4X is capable of representing all parts of an XML document by mapping each type, specifically
XMLList, to multiple DOM types.
The XML type is the most important new type introduced in E4X, because it can represent any single part of an XML structure. An instance of XML can represent an element, an attribute, a comment, a processing instruction, or a text node. The XML type inherits from the
Object type, so it inherits all of the default properties and methods of all objects. There are a few ways to create a new
XML object, the first of which is to ...