E4X

This article is in need of a technical review.

Obsolete
This feature is obsolete. Although it may still work in some browsers, its use is discouraged since it could be removed at any time. Try to avoid using it.

Warning: E4X is obsolete. It 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. Use DOMParser/DOMSerializer or a non-native JXON algorithm instead.

ECMAScript for XML (E4X) is a programming language extension that adds native XML support to JavaScript. It does this by providing access to the XML document in a form that feels natural for ECMAScript programmers. The goal is to provide an alternative, simpler syntax for accessing XML documents than via DOM interfaces. A valid alternative to E4X is a non-native JXON algorithm.

E4X is standardized by Ecma International in ECMA-357 standard (currently in its second edition, December 2005).

E4X is implemented (at least partially) in SpiderMonkey (Gecko's JavaScript engine) and in Rhino (JavaScript engine written in Java).

Note: In Gecko 1.8 based browsers such as Firefox 1.5, E4X is already partially enabled for web page authors. To fully enable E4X, the <script> element needs to have the MIME type "text/javascript;e4x=1" (i.e., have an attribute of the form type="text/javascript;e4x=1"). The difference between the two modes is that without the "e4x=1" MIME type, any statement-level XML/HTML comment literals (<!--...-->) are ignored for backwards compatibility with the comment hiding trick, and CDATA sections (<![CDATA[...]]>) are not parsed as CDATA literals (which leads to a JS syntax error in HTML since HTML's <script> element produces an implicit CDATA section, and therefore cannot contain explicit CDATA sections).

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Known bugs and limitations

  • It is not currently possible to access a DOM object through E4X (bug 270553).
  • E4X doesn't support parsing XML declaration.
  • <?xml version=...?>) (see bug 336551). You may get SyntaxError "xml is a reserved identifier" (despite the XML being in a string).

Workaround:

var response = xmlhttprequest.responseText; // bug 270553
response = response.replace(/^<\?xml\s+version\s*=\s*(["'])[^\1]+\1[^?]*\?>/, ""); // bug 336551
var e4x = new XML(response);

Resources

See also