(function(w, d){

  var dynamicContent = {

    'screen and (max-width: 240px)': 'This is a very tiny viewport!',

    'screen and (min-width: 241px) and (max-width: 640px)': 'Not tiny but still very small viewport!',

    'screen and (min-width: 641px)': 'Medium sized viewport'

  };

  w.addEventListener('load', function() {

    Object.keys(dynamicContent).forEach(function(mediaQuery) {

      var mql = w.matchMedia(mediaQuery);

      mql.addListener(function() {

        if(mql.matches) {

          d.querySelector('.container').innerHTML = dynamicContent[mediaQuery];

        }

      });

    });

  });

}(window, document));

​