function nunber(allowancePersonValue){

 if(allowancePersonValue=="身份证号"){

 $("#span_username").show();

 $("#span_username").html("身份证号不能为空");

 return false;

 }

 //校验长度，类型

 else if(isCardNo(allowancePersonValue) === false)

 {

$("#span_username").show();

 $("#span_username").html("您输入的身份证号码不正确，请重新输入");

 return false;

 }

 //检查省份

 else if(checkProvince(allowancePersonValue) === false)

 {

 $("#span_username").show();

 $("#span_username").html("您输入的身份证号码不正确,请重新输入");

 return false;

 }

 //校验生日

 else if(checkBirthday(allowancePersonValue) === false)

 {

 $("#span_username").show();

 $("#span_username").html("您输入的身份证号码生日不正确,请重新输入");

 return false;

 }

 //检验位的检测

 else if(checkParity(allowancePersonValue) === false)

 {

 $("#span_username").show();

 $("#span_username").html("您的身份证校验位不正确,请重新输入");

 return false;

 }else{

 $("#span_username").hide();

 return true;

 } 

} 

//身份证省的编码

var vcity={ 11:"北京",12:"天津",13:"河北",14:"山西",15:"内蒙古",

    21:"辽宁",22:"吉林",23:"黑龙江",31:"上海",32:"江苏",

    33:"浙江",34:"安徽",35:"福建",36:"江西",37:"山东",41:"河南",

    42:"湖北",43:"湖南",44:"广东",45:"广西",46:"海南",50:"重庆",

    51:"四川",52:"贵州",53:"云南",54:"*",61:"陕西",62:"甘肃",

    63:"青海",64:"宁夏",65:"*",71:"*",81:"香港",82:"澳门",91:"国外"

    }; 

//检查号码是否符合规范，包括长度，类型

function isCardNo(card){

 //身份证号码为15位或者18位，15位时全为数字，18位前17位为数字，最后一位是校验位，可能为数字或字符X

 var reg = /(^\d{15}$)|(^\d{17}(\d|X)$)/;

 if(reg.test(card) === false){

 //alert("demo");

 return false;

 }

 return true;

} 

//取身份证前两位,校验省份

function checkProvince(card){

 var province = card.substr(0,2);

 if(vcity[province] == undefined){

 return false;

 }

 return true;

} 

//检查生日是否正确

function checkBirthday(card){

 var len = card.length;

 //身份证15位时，次序为省（3位）市（3位）年（2位）月（2位）日（2位）校验位（3位），皆为数字

 if(len == '15'){

   var re_fifteen = /^(\d{6})(\d{2})(\d{2})(\d{2})(\d{3})$/;

   var arr_data = card.match(re_fifteen);

   var year = arr_data[2];

   var month = arr_data[3];var day = arr_data[4];var birthday =newDate('19'+year+'/'+month+'/'+day);return verifyBirthday('19'+year,month,day,birthday);}//身份证18位时，次序为省（3位）市（3位）年（4位）月（2位）日（2位）校验位（4位），校验位末尾可能为X if(len =='18'){var re_eighteen =/^(\d{6})(\d{4})(\d{2})(\d{2})(\d{3})([0-9]|X)$/;var arr_data = card.match(re_eighteen);var year = arr_data[2];var month = arr_data[3];var day = arr_data[4];var birthday =newDate(year+'/'+month+'/'+day);return verifyBirthday(year,month,day,birthday);}returnfalse;}//校验日期 function verifyBirthday(year,month,day,birthday){var now =newDate();var now_year = now.getFullYear();//年月日是否合理 if(birthday.getFullYear()== year &&(birthday.getMonth()+1)== month && birthday.getDate()== day){//判断年份的范围（3岁到100岁之间) var time = now_year - year;if(time >=3&& time <=100){returntrue;}returnfalse;}returnfalse;}//校验位的检测 function checkParity(card){//15位转18位

 card = changeFivteenToEighteen(card);var len = card.length;if(len =='18'){var arrInt =newArray(7,9,10,5,8,4,2,1,6,3,7,9,10,5,8,4,2);var arrCh =newArray('1','0','X','9','8','7','6','5','4','3','2');var cardTemp =0, i, valnum;for(i =0; i <17; i ++){

     cardTemp += card.substr(i,1)* arrInt[i];}

   valnum = arrCh[cardTemp %11];if(valnum == card.substr(17,1)){returntrue;}returnfalse;}returnfalse;}//15位转18位身份证号 function changeFivteenToEighteen(card){if(card.length =='15'){var arrInt =newArray(7,9,10,5,8,4,2,1,6,3,7,9,10,5,8,4,2);var arrCh =newArray('1','0','X','9','8','7','6','5','4','3','2');var cardTemp =0, i;

   card = card.substr(0,6)+'19'+ card.substr(6, card.length -6);for(i =0; i <17; i ++){

     cardTemp += card.substr(i,1)* arrInt[i];}

   card += arrCh[cardTemp %11];return card;}return card;}

<input type="text" class="reg_txt" value="身份证号" titles="请输入您的身份证号！" name="userid" id="username" maxlength="40" onfocus="if(this.value=='身份证号'){this.value='';}" onblur="if(this.value==''){this.value='身份证号';}nunber(this.value);" style="border: 1px solid red;"><br>

<span class="c_red" id="span_username"></span>