D3 Examples - Leaflet with a GeoJSON layer

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 <!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8">
    <title>A basic map with Leaflet</title>
    
    <!--add Leaflet CSS-->
     <link rel="stylesheet" href="https://unpkg.com/leaflet@1.3.1/dist/leaflet.css"
      integrity="sha512-Rksm5RenBEKSKFjgI3a41vrjkw4EVPlJ3+OiI65vTjIdo9brlAacEuKOiQ5OFh7cOI1bkDwLqdLw3Zg0cRJAAQ=="
      crossorigin=""/>
    
    <!--our own style rules-->
    <style type="text/css">
      body, html {
        height: 90%;
      }
      #map-container {
        height: 100%;
      }
    </style>
  </head>
  <body>
    
    <!--The div in which the map will be created-->
    <div id="map-container"></div>
    
    <!--load leaflet.js-->
    <script src="https://unpkg.com/leaflet@1.3.1/dist/leaflet.js"
    integrity="sha512-/Nsx9X4HebavoBvEBuyp3I7od5tA0UzAxs+j83KgC8PU0kgB4XiK4Lfe4y4cgBtaRJQEIFCW+oC506aPT2L1zw=="
    crossorigin=""></script>
    
    <!--our own code to create the map-->
    <script>
      let map = L.map('map-container');
      map.setView([52.268, 4.998], 7);
      let bglayer_Positron = L.tileLayer('https://cartodb-basemaps-{s}.global.ssl.fastly.net/light_all/{z}/{x}/{y}.png', {
        attribution: '&copy; <a href="https://www.openstreetmap.org/copyright">OpenStreetMap</a> &copy; <a href="https://cartodb.com/attributions">CartoDB</a>',
        subdomains: 'abcd',
        maxZoom: 19
      });
      
      bglayer_Positron.addTo(map);
      //define color of points based on earthquake type
      function colorPoints(type){
        return type === 'tec' ? '#35495D' :
          type === 'ind' ? '#EA9657' :
          '#317581'
      }
      //define how our point data will be visualized
      function styleEarthquakePoints(feature){
        return {
          radius: 2.5*Math.sqrt((Math.exp(parseFloat(feature.properties.MAG)))),
          fillColor: colorPoints(feature.properties.TYPE),
          color: '#fff',
          weight: 1,
          opacity: 0.8,
          fillOpacity: 0.6
        };
      }
      //create an empty geojson layer that already knows how to style the data
      var geojson = L.geoJson(null,{
        pointToLayer: function (feature, latlng) {
          return L.circleMarker(latlng, styleEarthquakePoints(feature));
        }
      }).addTo(map);
      //define a function to get and parse geojson from URL
      async function getGeoData(url) {
        let response = await fetch(url);
        let data = await response.json();
        return data;
      }
      
      //fetch the geojson and add it to our geojson layer
      getGeoData('aardbevingen_NL.geojson').then(data => geojson.addData(data));
    </script>
  </body>
</html>
​
    