次のような DOMParser を使用できます。
var pageStr = "<html><head></head><body><h1>Hello</h1><span>YO</span></body></html>";
var dp = new DOMParser();
var doc = dp.parseFromString(pageStr,'text/html');
alert(doc.documentElement.outerHTML);//"<html><head></head><body><h1>Hello</h1><span>YO</span></body></html>"
$(doc).find("span").remove();
alert($(doc).get(0).documentElement.outerHTML);//"<html><head></head><body><h1>Hello</h1></body></html>"
JSFiddle
更新: answer は DOMParser ポリフィルを実装するようになりました
/*
* DOMParser HTML extension
* 2012-09-04
*
* By Eli Grey, http://eligrey.com
* Public domain.
* NO WARRANTY EXPRESSED OR IMPLIED. USE AT YOUR OWN RISK.
*/
/*! @source https://gist.github.com/1129031 */
/*global document, DOMParser*/
(function(DOMParser) {
"use strict";
var
DOMParser_proto = DOMParser.prototype
, real_parseFromString = DOMParser_proto.parseFromString
;
// Firefox/Opera/IE throw errors on unsupported types
try {
// WebKit returns null on unsupported types
if ((new DOMParser).parseFromString("", "text/html")) {
// text/html parsing is natively supported
return;
}
} catch (ex) {}
DOMParser_proto.parseFromString = function(markup, type) {
if (/^\s*text\/html\s*(?:;|$)/i.test(type)) {
var
doc = document.implementation.createHTMLDocument("")
;
if (markup.toLowerCase().indexOf('<!doctype') > -1) {
doc.documentElement.innerHTML = markup;
}
else {
doc.body.innerHTML = markup;
}
return doc;
} else {
return real_parseFromString.apply(this, arguments);
}
};
}(DOMParser));