获取窗体可见范围的宽与高

function getViewSize() {
  var de = document.documentElement;
  var db = document.body;
  var viewW = de.clientWidth == 0 ? db.clientWidth : de.clientWidth;
  var viewH = de.clientHeight == 0 ? db.clientHeight : de.clientHeight;
  return Array(viewW, viewH);
}