讓div置中的方法

 var docWidth = document.body.offsetWidth;
        // var docHeight = document.body.offsetHeight;
       
        var divobj = document.getElementById("align");
        var divWidth = divobj.offsetWidth;
        // var divHeight = divobj.offsetHeight;
       
         //讓圖片左右置中顯示 
         var marginleft=(docWidth-divWidth)/2; 
         divobj.style.marginLeft = marginleft +"px"; 
        
         //讓圖片上下置中顯示 
         //var margintop=(docHeight-divHeight)/2; 
         //divobj.style.marginTop = margintop + "px";