(function(){
 var supportOrientation = (typeof window.orientation === 'number' &&
   typeof window.onorientationchange === 'object');//判断是否支持orientation 这个属性
 
 var init = function(){
  var htmlNode = document.body.parentNode,
   orientation;
  var updateOrientation = function(){
   if(supportOrientation){
    orientation = window.orientation;
    switch(orientation){
     case 90:
     case -90:
      orientation = 'landscape';//横屏
      break;
     default:
      orientation = 'portrait';//竖屏
      break;
    }
   }else{
    orientation = (window.innerWidth > window.innerHeight) ? 'landscape' : 'portrait';//解决兼容性问题
   }
   htmlNode.setAttribute('class',orientation);
  };
 
  if(supportOrientation){
   window.addEventListener('orientationchange',updateOrientation,false);
  }else{
   //监听resize事件
   window.addEventListener('resize',updateOrientation,false);
  }
 
  updateOrientation();
 };
 
 window.addEventListener('DOMContentLoaded',init,false);
})();