Standard library responsive.

gistfile1.js

<script type="text/javascript" charset="utf-8">
    var gptAdSlots = [];
    googletag.cmd.push(function() {
    
      // Define a size mapping object. The first parameter to addSize is
      // a viewport size, while the second is a list of allowed ad sizes.
      var mapping = googletag.sizeMapping().
      addSize([940, 200], [160, 600]).
      addSize([0,0], []).build();
    
      // Define the GPT slot
      gptAdSlots[0] = googletag.defineSlot('/6355419/travel', [160, 600], 'wideskyleft').
          defineSizeMapping(mapping).
          addService(googletag.pubads());
      googletag.pubads().setTargeting("test","responsive");
    
      // Start ad fetching
      googletag.enableServices();
      googletag.cmd.push(function() {
        googletag.display('wideskyleft');
      });
    });
    
    reloadAds: function(){
      googletag.cmd.push(function() {
        googletag.pubads().refresh([gptAdSlots[0]]);
      });
    };
    //reload ads on window resize, using jquery.throttle
    $(window).resize( $.throttle( 250, reloadAds ) );

</script>