Code snippet of tutorial running tracker

tracker.js

const drawNewSegment = (detail) => {
  
  const { latitude, longitude } = detail;

  return new Promise((resolve) => {
    if (path == null) {

      path = L.polyline([
        [ latitude, longitude ],
      ], {
        color: '#fbc531',
        bubblingMouseEvents: true
      }).addTo(map);

      map.setView([latitude, longitude], 15)
      map.fitBounds(path.getBounds());

    } else {

      if (isStart === true) {

        path._latlngs.push([latitude, longitude]);
        path.redraw();

      }
    }

    return resolve(detail);
  })
}