popup with dead link

index.js

var sampleFeature = {
      type: "Feature",
      properties: {
        Notes:
          "The closest entrance is on Seaman Avenue at Isham Street, and you'll find the run just behind the flag pole. You can reach Inwood Hill Park by Subway via the A train to 207th St, or the 1 train to 207th St, and walk west.",
        boro: "Manhattan",
        name: "Inwood Hill Park Dog Run: Homer's Run",
        Url: "http://www.inwoof.com/",
        state: "NY",
        address: "Seaman Avenue & Isham Street",
        DogRuns_Type: "Run",
        Accessible: "N",
        Prop_ID: "M042",
        postalCode: "10452"
      },
      geometry: {
        coordinates: [-73.921707, 40.871139],
        type: "Point"
      },
      id: "149478e1201a8c7aafe14a8133077a91"
    }  

// console.log('currentFeature: ', currentFeature);
  let extLink = currentFeature.properties.Url ? "<a target=\"_blank\" href=\"" + currentFeature.properties.Url + "\">External Link</a>" : ""
  // console.log('extLink: ', extLink);

  let popup = new mapboxgl.Popup({
    closeOnClick: false,
    anchor: "top",
    offset: [0, 20]
  })
    .setLngLat(currentFeature.geometry.coordinates)
    .setHTML(
    '<div id="popup" class="mapboxgl-popup"><div><h3>' +
    currentFeature.properties.name +
    "</h3>" +
    "<h4>" +
    currentFeature.properties.address +
    "</h4>" + extLink +
    notesEl +
    "</div>"
    )
    .addTo(map);
}