根据身份证号计算年龄

function getIdcardAge(idcard) {
  var len = (idcard + "").length;
  if (len == 0) {
    return 0;
  } else {
    if ((len != 15) && (len != 18)) {
      return 0;
    }
  }
  var strBirthday = "";
  if (len == 18) {
    strBirthday = idcard.substr(6, 4) + "/" + idcard.substr(10, 2) + "/" + idcard.substr(12, 2);
  }
  if (len == 15) {
    strBirthday = "19" + idcard.substr(6, 2) + "/" + idcard.substr(8, 2) + "/" + idcard.substr(10,
      2);
  }
  //时间字符串里，必须是“/”
  var birthDate = new Date(strBirthday);
  var nowDateTime = new Date();
  var age = nowDateTime.getFullYear() - birthDate.getFullYear();
  //再考虑月、天的因素;.getMonth()获取的是从0开始的，这里进行比较，不需要加1
  if (nowDateTime.getMonth() < birthDate.getMonth() || (nowDateTime.getMonth() == birthDate.getMonth() && nowDateTime
    .getDate() < birthDate.getDate())) {
    age--;
  }
  return age;
}