var map = new ol.Map({
  layers: [
    new ol.layer.Tile({
      source: new ol.source.OSM()
    })
  ],
  target: 'map',
  controls: ol.control.defaults({
    attributionOptions: /** @type {olx.control.AttributionOptions} */ ({
      collapsible: false
    })
  }),
  view: new ol.View({
    center: [0, 0],
    zoom: 2
  })
});

function display(id, value) {
  document.getElementById(id).value = value.toFixed(2);
}

function wrapLon(value) {
  var worlds = Math.floor((value + 180) / 360);
  return value - (worlds * 360);
}

function onMoveEnd(evt) {
  var map = evt.map;
  var extent = map.getView().calculateExtent(map.getSize());
  var bottomLeft = ol.proj.transform(ol.extent.getBottomLeft(extent),
      'EPSG:3857', 'EPSG:4326');
  var topRight = ol.proj.transform(ol.extent.getTopRight(extent),
      'EPSG:3857', 'EPSG:4326');
  display('left', wrapLon(bottomLeft[0]));
  display('bottom', bottomLeft[1]);
  display('right', wrapLon(topRight[0]));
  display('top', topRight[1]);
}

map.on('moveend', onMoveEnd);
