D3 Examples - simple spinning loader

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<!DOCTYPE html>
<html>
​
<head>
    <meta charset=utf-8 />
    <title>Loading Screen Example</title>
    <meta name='viewport' content='initial-scale=1,maximum-scale=1,user-scalable=no' />
​
    <script src="https://cdnjs.cloudflare.com/ajax/libs/leaflet/0.7.3/leaflet.min.js"></script>
    <script src="https://code.jquery.com/jquery-2.1.4.min.js"></script>
​
    <link rel="stylesheet" href="https://cdn.leafletjs.com/leaflet-0.7.3/leaflet.css" />
    <link href='https://fonts.googleapis.com/css?family=Lato' rel='stylesheet' type='text/css'>
​
    <style>
        body {
            margin: 0;
            padding: 0;
            background: whitesmoke;
            font-family: Lato, sans-serif;
            color: #0D0000;
        }
        #map {
            position: absolute;
            top: 0;
            bottom: 0;
            width: 100%;
            z-index: 100;
        }
        
/*       have the loader div fill the map screen while disabling interaction */
        #loader {
            position: absolute;
            top: 0;
            bottom: 0;
            width: 100%;
            background-color: rgba(245, 245, 245, 0.7);
            z-index: 200;
        }
        
/*       since we know the height/width of the loader gif, 
         position absolutely and use top/left, subtracting half of 
         width and heigth using margin */
        #loader img {
            width: 66px;
            height: 66px;
            position: absolute;
            top: 50%;
            left: 50%;
            margin: -33px 0 0 -33px;
        }
    </style>
</head>
​
<body>
​
    <div id='map'>
<!--    loader div with opaque background-->
        <div id='loader'>
<!--        animated gif of spinning loader-->
            <img src='loader.gif' alt='loader' />
        </div>
    </div>
   
    <script>
​
        var map = L.map('map', {
            center: [42,-95],
            zoom: 4
        });
        
        var tiles = L.tileLayer('https://a{s}.acetate.geoiq.com/tiles/acetate-hillshading/{z}/{x}/{y}.png', {
            attribution: '&copy;2012 Esri & Stamen, Data from OSM and Natural Earth',
            subdomains: '0123',
            minZoom: 2,
            maxZoom: 18
        });
        
        // let's request the tiles and let them load as they do
        map.addLayer(tiles);
        
        // request to load large file asychronously
        $.getJSON('https://rgdonohue.github.io/data/rails.json', function(data){
        
           // when the data are ready
           ready(data);
            
        });
        
        function ready(data){
            
            // remove the loader div from the DOM
            $('#loader').remove();
            
            // do stuff with the data
            L.geoJson(data).addTo(map);
    
        }
​
    </script>
    
</body>
​
</html>
    