Feature Collection Parsing

Parse a feature collection contained in a webmap to GeoJSON.
<!DOCTYPE html>
<html>
<head>
  <meta charset="utf-8" />
  <title>Feature Collection Parsing</title>
  <meta name="viewport" content="initial-scale=1,maximum-scale=1,user-scalable=no" />

  <!-- Load Leaflet from CDN -->
  <link rel="stylesheet" href="https://unpkg.com/leaflet@1.7.1/dist/leaflet.css"
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    crossorigin=""/>
  <script src="https://unpkg.com/leaflet@1.7.1/dist/leaflet.js"
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    crossorigin=""></script>

  <!-- Load Esri Leaflet from CDN -->
  <script src="https://unpkg.com/esri-leaflet@3.0.8/dist/esri-leaflet.js"
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    crossorigin=""></script>

  <!-- Load Esri Leaflet Vector from CDN -->
  <script src="https://unpkg.com/esri-leaflet-vector@4.0.0/dist/esri-leaflet-vector.js"
    integrity="sha512-EMt/tpooNkBOxxQy2SOE1HgzWbg9u1gI6mT23Wl0eBWTwN9nuaPtLAaX9irNocMrHf0XhRzT8B0vXQ/bzD0I0w=="
    crossorigin=""></script>

  <style>
    body { margin:0; padding:0; }
    #map { position: absolute; top:0; bottom:0; right:0; left:0; }
  </style>
</head>
<body>

<div id="map"></div>

<script>
  var map = L.map('map');
  L.esri.Vector.vectorBasemapLayer('OSM:StreetsRelief', {
    apikey: apiKey // Replace with your API key - https://developers.arcgis.com
  }).addTo(map);

  L.esri.get('https://www.arcgis.com/sharing/content/items/62914b2820c24d4e95710ebae77937cb/data', {}, function (error, response) {
    if (error) {
      return;
    }

    var features = response.operationalLayers[0].featureCollection.layers[0].featureSet.features;
    var idField = response.operationalLayers[0].featureCollection.layers[0].layerDefinition.objectIdField;

    // empty geojson feature collection
    var featureCollection = {
      type: 'FeatureCollection',
      features: []
    };

    for (var i = features.length - 1; i >= 0; i--) {
      // convert ArcGIS Feature to GeoJSON Feature
      var feature = L.esri.Util.arcgisToGeoJSON(features[i], idField);

      // unproject the web mercator coordinates to lat/lng
      var latlng = L.Projection.Mercator.unproject(L.point(feature.geometry.coordinates));
      feature.geometry.coordinates = [latlng.lng, latlng.lat];

      featureCollection.features.push(feature);
    }

    var geojson = L.geoJSON(featureCollection).addTo(map);
    map.fitBounds(geojson.getBounds());
  });
</script>

</body>
</html>
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