Timezones in KML

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/*
 * Compute the style of the feature.  Here we want the opacity of polygons to
 * be based on the offset from local noon.  For example, a timezone where it is
 * currently noon would have an opacity of 0.75.  And a timezone where it is
 * currently midnight would have an opacity of 0.  This doesn't account for
 * daylight savings, so don't use it to plan your vacation.
 */
var styleFunction = function(feature) {
  var offset = 0;
  var name = feature.get('name'); // e.g. GMT -08:30
  var match = name.match(/([\-+]\d{2}):(\d{2})$/);
  if (match) {
    var hours = parseInt(match[1], 10);
    var minutes = parseInt(match[2], 10);
    offset = 60 * hours + minutes;
  }
  var date = new Date();
  var local = new Date(date.getTime() +
      (date.getTimezoneOffset() + offset) * 60000);
  // offset from local noon (in hours)
  var delta = Math.abs(12 - local.getHours() + (local.getMinutes() / 60));
  if (delta > 12) {
    delta = 24 - delta;
  }
  var opacity = 0.75 * (1 - delta / 12);
  return new ol.style.Style({
    fill: new ol.style.Fill({
      color: [0xff, 0xff, 0x33, opacity]
    }),
    stroke: new ol.style.Stroke({
      color: '#ffffff'
    })
  });
};

var vector = new ol.layer.Vector({
  source: new ol.source.Vector({
    url: 'https://openlayers.org/en/v4.6.4/examples/data/kml/timezones.kml',
    format: new ol.format.KML({
      extractStyles: false
    })
  }),
  style: styleFunction
});

var raster = new ol.layer.Tile({
  source: new ol.source.Stamen({
    layer: 'toner'
  })
});

var map = new ol.Map({
  layers: [raster, vector],
  target: 'map',
  view: new ol.View({
    center: [0, 0],
    zoom: 2
  })
});

var info = $('#info');
info.tooltip({
  animation: false,
  trigger: 'manual'
});

map.on('pointermove', function(evt) {
  if (evt.dragging) {
    info.tooltip('hide');
    return;
  }
  displayFeatureInfo(map.getEventPixel(evt.originalEvent));
});

map.on('click', function(evt) {
  displayFeatureInfo(evt.pixel);
});

<!DOCTYPE html>
<html>
  <head>
    <title>Timezones in KML</title>
    <link rel="stylesheet" href="https://openlayers.org/en/v4.6.4/css/ol.css" type="text/css">
    <!-- The line below is only needed for old environments like Internet Explorer and Android 4.x -->
    <script src=""></script>
    <script src="https://openlayers.org/en/v4.6.4/build/ol.js"></script>
    <script src="https://code.jquery.com/jquery-2.2.3.min.js"></script>
    <link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.6/css/bootstrap.min.css">
    <script src="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.6/js/bootstrap.min.js"></script>
    <style>
      #map {
        position: relative;
      }
      #info {
        position: absolute;
        height: 1px;
        width: 1px;
        z-index: 100;
      }
    </style>
  </head>
  <body>
    <div id="map" class="map"><div id="info"></div></div>
    <script>
      /*
       * Compute the style of the feature.  Here we want the opacity of polygons to
       * be based on the offset from local noon.  For example, a timezone where it is
       * currently noon would have an opacity of 0.75.  And a timezone where it is
       * currently midnight would have an opacity of 0.  This doesn't account for
       * daylight savings, so don't use it to plan your vacation.
       */
      var styleFunction = function(feature) {
        var offset = 0;
        var name = feature.get('name'); // e.g. GMT -08:30
        var match = name.match(/([\-+]\d{2}):(\d{2})$/);
        if (match) {
          var hours = parseInt(match[1], 10);
          var minutes = parseInt(match[2], 10);
          offset = 60 * hours + minutes;
        }
        var date = new Date();
        var local = new Date(date.getTime() +
            (date.getTimezoneOffset() + offset) * 60000);
        // offset from local noon (in hours)
        var delta = Math.abs(12 - local.getHours() + (local.getMinutes() / 60));
        if (delta > 12) {
          delta = 24 - delta;
        }
        var opacity = 0.75 * (1 - delta / 12);
        return new ol.style.Style({
          fill: new ol.style.Fill({
            color: [0xff, 0xff, 0x33, opacity]
          }),
          stroke: new ol.style.Stroke({
            color: '#ffffff'
          })
        });
      };

      var vector = new ol.layer.Vector({
        source: new ol.source.Vector({
          url: 'https://openlayers.org/en/v4.6.4/examples/data/kml/timezones.kml',
          format: new ol.format.KML({
            extractStyles: false
          })
        }),
        style: styleFunction
      });

      var raster = new ol.layer.Tile({
        source: new ol.source.Stamen({
          layer: 'toner'
        })
      });

      var map = new ol.Map({
        layers: [raster, vector],
        target: 'map',
        view: new ol.View({
          center: [0, 0],
          zoom: 2
        })
      });

      var info = $('#info');
      info.tooltip({
        animation: false,
        trigger: 'manual'
      });

      var displayFeatureInfo = function(pixel) {
        info.css({
          left: pixel[0] + 'px',
          top: (pixel[1] - 15) + 'px'
        });
        var feature = map.forEachFeatureAtPixel(pixel, function(feature) {
          return feature;
        });
        if (feature) {
          info.tooltip('hide')
              .attr('data-original-title', feature.get('name'))
              .tooltip('fixTitle')
              .tooltip('show');
        } else {
          info.tooltip('hide');
        }
      };

      map.on('pointermove', function(evt) {
        if (evt.dragging) {
          info.tooltip('hide');
          return;
        }
        displayFeatureInfo(map.getEventPixel(evt.originalEvent));
      });

      map.on('click', function(evt) {
        displayFeatureInfo(evt.pixel);
      });
    </script>
  </body>
</html>