弹出div显示遮罩层的效果，想必大家都有见到过吧，下面有个示例，大家可以参考下

 代码如下: //--------------------弹出层-------------------  //popDivId:弹出层div的ID  //dragDivId:用于拖动div的ID  //isShowMask:是否显示遮罩层  function popDivShow(popDivId, dragDivId, isShowMask) {  if (isShowMask) {  creatMask(popDivId);  }  var oWins = document.getElementById(popDivId);  var oWins_title = document.getElementById(dragDivId);  var bDrag = false;  var disX = disY = 0;  oWins.style.display = "block";  oWins_title.onmousedown = function(event) {  var event = event || window.event;  bDrag = true;  disX = event.clientX - oWins.offsetLeft;  disY = event.clientY - oWins.offsetTop;  this.setCapture && this.setCapture();  return false;  };  document.onmousemove = function(event) {  if (!bDrag)  return;  var event = event || window.event;  var iL = event.clientX - disX;  var iT = event.clientY - disY;  var maxL = document.documentElement.clientWidth - oWins.offsetWidth;  var maxT = document.documentElement.clientHeight - oWins.offsetHeight;  iL = iL < 0 ? 0 : iL;  iL = iL > maxL ? maxL : iL;  iT = iT < 0 ? 0 : iT;  iT = iT > maxT ? maxT : iT;  oWins.style.marginTop = oWins.style.marginLeft = 0;  oWins.style.left = iL + "px";  oWins.style.top = iT + "px";  return false;  };  document.onmouseup = window.onblur = oWins_title.onlosecapture = function() {  bDrag = false;  oWins_title.releaseCapture && oWins_title.releaseCapture();  };  }  // 隐藏弹出层  function popDivHidden(popDivId) {  var oWins = document.getElementById(popDivId);  oWins.style.display = "none";  window.parent.document.body.removeChild(window.parent.document.getElementById("maskDiv"));  }  // 获取弹出层的zIndex  function getZindex(popDivId) {  var popDiv = document.getElementById(popDivId);  var popDivZindex = popDiv.style.zIndex;  return popDivZindex;    }  // 创建遮罩层  function creatMask(popDivId) {  // 参数w为弹出页面的宽度,参数h为弹出页面的高度,参数s为弹出页面的路径  var maskDiv = window.parent.document.createElement("div");  maskDiv.id = "maskDiv";  maskDiv.style.position = "fixed";  maskDiv.style.top = "0";  maskDiv.style.left = "0";  maskDiv.style.zIndex = getZindex(popDivId) - 1;  maskDiv.style.backgroundColor = "#333";  maskDiv.style.filter = "alpha(opacity=70)";  maskDiv.style.opacity = "0.7";  maskDiv.style.width = "100%";  maskDiv.style.height = (window.parent.document.body.scrollHeight + 50) + "px";  window.parent.document.body.appendChild(maskDiv);  maskDiv.onmousedown = function() {  window.parent.document.body.removeChild(window.parent.document.getElementById("maskDiv"));  };  }