javascript 对表格的操作和window.open居中

javascript对表格的操作:
function addTr()
{      
          var table = document.getElementById("apntable");
          var lastTr = table.firstChild.lastChild;
          if(lastTr.id == "lastLineStyleTr") {
          lastTr.parentNode.removeChild(lastTr);
          }
  var input1 = document.createElement("input");
  var row1 = table.insertRow(-1);
  var row1_cell1 = row1.insertCell(-1);
   
  row1_cell1.className = "tdlineleft";
   
  row1_cell1.innerHTML = "<input id='apnname' name='apnname' size='6'></input>";
  table.firstChild.appendChild(lastTr);//table有个隐藏的属性<tbody>所以要在table加入一行应该table.firstChild.appendChild(row)
                    i++;
}

window.open居中:

function changepassword(url,height,width)
{
       screenX = window.screen.width;
       screenY = window.screen.height;
       var x = (screenX-width)/2;
       var y = (screenY-height)/2;
       window.open(url,null,"menubar:no,status:no,height:"+height+",width:"+width+",top="+y+",left="+x);
}

对于页面登录界面居中：

function showPosition() {
var windowHeight = document.body.offsetHeight;
var windowWidth = document.body.offsetWidth;
var loginDialog = document.getElementById("loginDialog");
var login = document.getElementById("login");
var loginHeight = login.offsetHeight;
var loginWidth = login.offsetWidth;
loginDialog.style.paddingLeft = (windowWidth - loginWidth)/2;
loginDialog.style.paddingTop = (windowHeight - loginHeight) / 3;

    window.onresize = showPosition;
    }