Check for XML errors using JavaScript

You can also use the package fast-xml-parser, this package have a validate check for xml files:

import { validate, parse } from 'fast-xml-parser';

if( validate(xmlData) === true) {
  var jsonObj = parse(xmlData,options);
}

NoBugs answer above did not work with a current chrome for me. I suggest:

var sMyString = "<a id=\"a\"><b id=\"b\">hey!<\/b><\/a>";
var oParser = new DOMParser();
var oDOM = oParser.parseFromString(sMyString, "text/xml");
dump(oDOM.getElementsByTagName('parsererror').length ? 
     (new XMLSerializer()).serializeToString(oDOM) : "all good"    
);

Edit: Here is a more concise example, from MDN:

var xmlString = '<a id="a"><b id="b">hey!</b></a>';
var domParser = new DOMParser();
var dom = domParser.parseFromString(xmlString, 'text/xml');

// print the name of the root element or error message
dump(dom.documentElement.nodeName == 'parsererror' ? 'error while parsing' : dom.documentElement.nodeName);