DOMParser HTML extension - Now a polyfill since HTML parsing was added to the DOMParser specification

html-domparser.js

/*
 * DOMParser HTML extension
 * 2019-11-13
 * 
 * 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;
	var 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("");
	      		doc.documentElement.innerHTML = markup;
			return doc;
		} else {
			return real_parseFromString.apply(this, arguments);
		}
	};
}(DOMParser));

I add this code In my scripts files and works fine but this code run several times , How can i prevent this ? maybe some codes simlar below codes

DOMParserFlag = false;
if (DOMParserFlag == false) {

function DOMParser() {
    "use strict";

..........

}
DOMParserFlag = true;

}

https://gist.github.com/1129031

Setting .innerHTML will load image ressources (even if element is not appended to DOM), which is not the case with DOMParser.

I remove this

if (markup.toLowerCase().indexOf('<!doctype') > -1) {
        console.log(markup);
        console.log('inserindo o elemento doc \n\n');
        //doc.documentElement.innerHTML = markup;
        doc.body.innerHTML = markup;
      } else {
        doc.body.innerHTML = markup;
      }

and i changed for this

doc.body.innerHTML = markup;

and I got the result I needed.

@kube I tested and it seems that using document.implementation.createHTMLDocument("") creates a new document, which not being attached to any window prevents arbitrary execution of anything (at least in the latest Chrome):

var doc = document.implementation.createHTMLDocument("")
doc.documentElement.innerHTML = '<img src="ERROR" onerror="console.log(456)" />'