E4x

ECMAScript for XML (E4X) is a programming language extension that adds native XML support to ECMAScript (which includes ActionScript, JavaScript, and JScript). The goal is 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. Before the release of E4X, XML was always accessed at an object level. E4X instead treats XML as a primitive (like characters, integers, and booleans). This implies faster access, better support, and acceptance as a building block (data structure) of a program.

E4X is standardized by ECMA-357 standard. The first edition was published in June 2004, the second edition in December 2005.

Browser support

E4X is supported by Mozilla's Rhino, used in OpenOffice.org and several other projects. It is also supported by Tamarin, the JavaScript engine used in the Flash virtual machine. It is not supported by other common engines like Nitro (Safari), V8 (Google Chrome), Carakan (Opera), nor Internet Explorer.[1]

E4X was also supported by SpiderMonkey (used in Firefox and Thunderbird), but has been removed. In Firefox 10, E4X syntax was no longer accepted in SpiderMonkey when ECMAStrict 5 "strict mode" is enabled.[2] According to Brendan Eich, "This thus signals start of deprecation for E4X in SpiderMonkey."[3] and "has been disabled by default for webpages (content) in Firefox 17, disabled by default for chrome in Firefox 20, and has been removed in Firefox 21"[4]

Example

var sales = 
    4" quantity="6"/>
    3" quantity="10"/>
    5" quantity="3"/>
  ;
 
alert( sales.item.(@type == "carrot").@quantity );
alert( sales.@vendor );
for each( var price in sales..@price ) {
  alert( price );
}
delete sales.item[0];
sales.item += 4"/>;
sales.item.(@type == "oranges").@quantity = 4;

Implementations

The first implementation of E4X was designed by Terry Lucas and John Schneider and appeared in article on the XML extensions in BEA's Workshop at the time.

  • E4X was implemented in SpiderMonkey (Gecko's JavaScript engine) since version 1.6.0[5] until version 20, and is in Rhino (Mozilla's other JavaScript engine written in Java instead of C) since version 1.6R1.[6]
  • As Mozilla Firefox is based on Gecko, older versions could be used to run scripts using E4X. But this feature is deprecated since release 16 and removed in release 18.
  • Adobe's ActionScript 3 scripting language fully supports E4X. Early previews of ActionScript 3 were first made available in late 2005. Adobe officially released the language with Flash Player 9 on June 28, 2006.
  • 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.
  • E4X is also available in Aptana's Jaxer Ajax application server which uses the Mozilla engine server-side.
  • Since the release of Alfresco Community Edition 2.9B, E4X is also available in this enterprise document management system.
  • E4X is available as part of Mirth Connect's JavaScript message transformation engine.

References

External links

  • ECMA-357 standard
  • E4X at faqts.com
  • Slides from 2005 E4X Presentation by Brendan Eich, Mozilla Chief Architect
  • E4X at Mozilla Developer Center
  • Introducing E4X at xml.com: compares E4X and json
  • Processing XML with E4X at Mozilla Developer Center
  • E4X: Beginner to Advanced at Yahoo Developer Network
  • Product showing E4X in action at Script Scraper.
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