How to extract an attribute using xml-fast-parser

I can extract elements from parsed XML like so:

import { XMLParser } from "fast-xml-parser";

let xml = '<gpx myAttr="fred"><trk>track 1</trk><trk>track 2<trkpt>trackpoint 2</trkpt></trk></gpx>';
const options = {
  ignoreAttributes: false,
  attributeNamePrefix : "@_"
};
const parser = new XMLParser(options);
const root = parser.parse(xml);

const track0 = root.gpx.trk[0];           // gives 'track 1'
const trackpoint = root.gpx.trk[1].trkpt; // gives 'trackpoint 2'
const attr = root.gpx.myAttr;             // gives 'undefined'

but trying to get the attribute doesn’t work. Because of the parser’s attributeNamePrefix I have also tried

 const attr = root.gpx.@_myAttr;

but of course that gives a syntax error. After I extract an attribute I want to modify it and recreate the XML using XMLBuilder, so I will need something like

root.gpx.myAttr = "newAttr";

There a JSFiddle here.

>Solution :

The code you put into JSFiddle seems mostly correct. However, there is a syntax error in the XML string; the closing tag for <trk> is missing. Here’s the corrected code:

Corrected JSFiddle:

// let xml = '<gpx myAttr="fred"><trk>track 1</trk><trk>track 2<trkpt>trackpoint 2</trkpt></trk></gpx>';
let xml =
  '<gpx myAttr="fred"><trk>track 1</trk><trk>track 2</trk><trkpt>trackpoint 2</trkpt></trk></gpx>';
const options = {
  ignoreAttributes: false,
  attributeNamePrefix: '@_', // you have assign this so use this to access the attribute
};
const parser = new XMLParser(options);
const root = parser.parse(xml);

const track0 = root.gpx.trk[0];
const trackpoint = root.gpx.trk[1].trkpt;
// const attr = root.gpx.myAttr
const attr = root.gpx['@_myAttr']; // Use the correct attribute name

document.getElementById('trk1').innerHTML = track0;
document.getElementById('trk2').innerHTML = trackpoint;
document.getElementById('attr').innerHTML = attr;

Changes made:

1. Corrected the missing closing tag for in the xml string.
2. Used root.gpx['@_myAttr'] instead of root.gpx.myAttr to access the attribute with the correct name.