Alternative to adaptjs (http://adapt.960.gs/)

gistfile1.js

(function(w,d, ranges) {
  var html = document.documentElement
  
  window.onresize = function() {
    var width = w.innerWidth || d.documentElement.clientWidth || d.body.clientWidth || 0;

    for (var i=0; i < ranges.length; i++) {
      if (ranges[i] < width) {      
        break;
      };
    };
    
    html.className = "js zoom-width-" + (i+1);
    
  };

  window.onresize();
})(window, document, [0, 1280, 1420, 1560, 1700, 1840, 1980, 2120, 5000]);