vector-layer.js

var style = new ol.style.Style({
  fill: new ol.style.Fill({
    color: 'rgba(255, 255, 255, 0.6)'
  }),
  stroke: new ol.style.Stroke({
    color: '#319FD3',
    width: 1
  }),
  text: new ol.style.Text({
    font: '12px Calibri,sans-serif',
    fill: new ol.style.Fill({
      color: '#000'
    }),
    stroke: new ol.style.Stroke({
      color: '#fff',
      width: 3
    })
  })
});
var styles = [style];
var vectorLayer = new ol.layer.Vector({
  source: new ol.source.GeoJSON({
    projection: 'EPSG:3857',
    url: 'geojson.json'
  }),
  style: function(feature, resolution) {
    style.getText().setText(resolution < 5000 ? feature.get('name') : '');
    return styles;
  }
});

var map = new ol.Map({
  layers: [
    new ol.layer.Tile({
      source: new ol.source.MapQuest({layer: 'sat'})
    }),
    vectorLayer
  ],
  target: 'map',
  view: new ol.View({
    center: [0, 0],
    zoom: 1
  })
});

var highlightStyleCache = {};

var featureOverlay = new ol.FeatureOverlay({
  map: map,
  style: function(feature, resolution) {
    var text = resolution < 5000 ? feature.get('name') : '';
    if (!highlightStyleCache[text]) {
      highlightStyleCache[text] = [new ol.style.Style({
        stroke: new ol.style.Stroke({
          color: '#f00',
          width: 1
        }),
        fill: new ol.style.Fill({
          color: 'rgba(255,0,0,0.1)'
        }),
        text: new ol.style.Text({
          font: '12px Calibri,sans-serif',
          text: text,
          fill: new ol.style.Fill({
            color: '#000'
          }),
          stroke: new ol.style.Stroke({
            color: '#f00',
            width: 3
          })
        })
      })];
    }
    return highlightStyleCache[text];
  }
});

var highlight;
var displayFeatureInfo = function(pixel) {

  var feature = map.forEachFeatureAtPixel(pixel, function(feature, layer) {
    return feature;
  });

  var info = document.getElementById('info');
  if (feature) {
    info.innerHTML = feature.getId() + ': ' + feature.get('name');
  } else {
    info.innerHTML = '&nbsp;';
  }

  if (feature !== highlight) {
    if (highlight) {
      featureOverlay.removeFeature(highlight);
    }
    if (feature) {
      featureOverlay.addFeature(feature);
    }
    highlight = feature;
  }

};

map.on('pointermove', function(evt) {
  if (evt.dragging) {
    return;
  }
  var pixel = map.getEventPixel(evt.originalEvent);
  displayFeatureInfo(pixel);
});

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