ol3_style_function.js

var styleFunction = (function () {

  var fill       = new ol.style.Fill({ color: 'rgba(255, 255, 255, 0.5)' }),
      stroke     = new ol.style.Stroke({ color: '#319FD3', width: 1 }),
      textFill   = new ol.style.Fill({ color: '#000' }),
      textStroke = new ol.style.Stroke({ color: '#fff', width: 3 }),
      cache      = {};
  
  return function (feature, resolution) {
    var text = resolution < 5000 ? feature.get('name') : '';
    if (cache[text]) {
      return cache[text]
    }
    var style = cache[text] = new ol.style.Style({
      fill   : fill,
      stroke : stroke,
      text   : new ol.style.Text({
        font   : '12px Calibri,sans-serif',
        text   : text,
        fill   : textFill,
        stroke : textStroke
      })
    });
    return style;
  };
});