校验是不是为正确格式的身份证号

校验是否为正确格式的身份证号
/**
*校验是否为正确格式的身份证号
*/
function isIdenCard(num){  //num是传进来的身份证号  调用此方法即可   通过返回true false
if (isNaN(num)) {
$("#messageBox").html("<s:text name='doent.chainse'/>");
$("#messageBox").css("color","red");
$("#messageBox").show();
return false;}
    var len = num.length, re;
    if (len == 15)
      re = new RegExp(/^(\d{6})()?(\d{2})(\d{2})(\d{2})(\d{3})$/);
    else if (len == 18)
      re = new RegExp(/^(\d{6})()?(\d{4})(\d{2})(\d{2})(\d{3})(\d)$/);
    else {
    $("#messageBox").html("<s:text name='content.length.number'/>");
    $("#messageBox").css("color","red");
$("#messageBox").show();
        return false;}
    var a = num.match(re);
    if (a != null)
    {
      if (len==15)
      {
        var D = new Date("19"+a[3]+"/"+a[4]+"/"+a[5]);
        var B = D.getYear()==a[3]&&(D.getMonth()+1)==a[4]&&D.getDate()==a[5];
      }
      else
      {
        var D = new Date(a[3]+"/"+a[4]+"/"+a[5]);
        var B = D.getFullYear()==a[3]&&(D.getMonth()+1)==a[4]&&D.getDate()==a[5];
      }
    }
    return true;
  }