移动页面 REM自适应

 ~function(){
         let computed = function(){
         let desW = 640;
         let devW = document.documentElement.clientWidth;
         if(devW>=640){
            document.documentElement.style.fontSize = '100px';
            return;
         }
         document.documentElement.style.fontSize = devW / desW * 100 + 'px';
         }
         computed();
         window.addEventListener('resize',computed,false);
     }();