已废弃
This feature is obsolete.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已经过时.从Firefox 17开始,E4X在普通网页中被默认禁用,从Firefox 20开始,E4X在浏览器界面中被默认禁用,从Firefox 21开始,E4X被完全删除.使用DOMParser/DOMSerializer或者其他算法来代替.
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).
<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).
someone verify the above
Workaround:
var response = xmlhttprequest.responseText; // bug 270553 response = response.replace(/^<\?xml\s+version\s*=\s*(["'])[^\1]+\1[^?]*\?>/, ""); // bug 336551 var e4x = new XML(response);