OpenLayers 3 Beginner’s Guide

Using ol.interaction.Modify to update drawing

<!doctype html>
<html>
  <head>
    <title>Modify sample</title>
    <link rel="stylesheet" href="../assets/ol3/css/ol.css" type="text/css" />
    <link rel="stylesheet" href="../assets/css/samples.css" type="text/css" />
  </head>
  <body>
    <div id="map" class="map"></div>
    <script src="../assets/ol3/js/ol.js"></script>
    <script>

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

      var selectEuropa = new ol.style.Style({
          stroke: new ol.style.Stroke({
          color: '#ff0000',
          width: 2
        })
      });

      var defaultEuropa = new ol.style.Style({
        stroke: new ol.style.Stroke({
          color: '#0000ff',
          width: 2
        })
      });

      var vectorEuropa = new ol.layer.Vector({
        id: 'europa',
        source: new ol.source.GeoJSON({
          projection: 'EPSG:3857',
          url: '../assets/data/nutsv9_lea.geojson'
        }),
        style: defaultEuropa
      });

      var selectInteraction = new ol.interaction.Select({
        condition: ol.events.condition.singleClick,
        toggleCondition: ol.events.condition.shiftKeyOnly,
        layers: function (layer) {
          return layer.get('id') == 'europa';
        },
        style: selectEuropa
      });

      var modify = new ol.interaction.Modify({
        features: selectInteraction.getFeatures()
      });

      var london = ol.proj.transform([-0.12755, 51.507222], 'EPSG:4326', 'EPSG:3857');

      var view = new ol.View({
        center: london,
        zoom: 6
      });

      var map = new ol.Map({
        target: 'map'
      });

      map.addLayer(raster);
      map.addLayer(vectorEuropa);
      map.setView(view);

      map.getInteractions().extend([selectInteraction, modify]);

      var selected_features = selectInteraction.getFeatures();

      var dirty = {};

      selected_features.on('add', function(evt) {
        var feature = evt.element;
        var fid = feature.getId();
        feature.on('change', function(evt) {
          dirty[evt.target.getId()] = true;
        });
      });

      selected_features .on('remove', function(evt) {
        var feature = evt.element;
        var fid = feature.getId();
        if (dirty[fid]) {
          console.log('changed');
        }
      });
    </script>
  </body>
</html>