leaflet map

<!DOCTYPE html>
<head>
  <meta charset="utf-8">
  <script src="https://cdnjs.cloudflare.com/ajax/libs/d3/3.5.5/d3.min.js"></script>
  <link rel="stylesheet" href="https://cdn.leafletjs.com/leaflet/v0.7.7/leaflet.css" />
   <script src="https://cdnjs.cloudflare.com/ajax/libs/leaflet/0.7.7/leaflet.min.js"></script>
  
  <style>
    body { margin:0;position:fixed;top:0;right:0;bottom:0;left:0; }
    #map {
      height: 100%;
    }
  </style>
</head>

<body>
  <div id="map"></div>
  <script>
    var map = L.map('map').setView([30, 0], 2);

L.tileLayer('https://{s}.tile.osm.org/{z}/{x}/{y}.png', {
        attribution: '&copy; <a href="https://osm.org/copyright">OpenStreetMap</a> contributors'
    }).addTo(map);
    
    //var url = "https://enjalot.github.io/wwsd/data/world/ne_50m_rivers_lake_centerlines.geojson"
    var url = "ne_50m_populated_places_simple.geojson"
    d3.json(url, function(err, geojson) {
      
      console.log("geojson data:", geojson);
      L.geoJson(geojson).addTo(map);
      
    })
    
  </script>
</body>

Modified http://cdn.leafletjs.com/leaflet/v0.7.7/leaflet.js to a secure url

https://cdnjs.cloudflare.com/ajax/libs/d3/3.5.5/d3.min.js

https://cdn.leafletjs.com/leaflet/v0.7.7/leaflet.js