JS实现短信验证码倒计时：解决页面刷新与关闭问题

<!doctype html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="Generator" content="EditPlus®">
<meta name="Author" content="">
<meta name="Keywords" content="">
<meta name="Description" content="">
<title>Document</title>
<script src="http://cdn.bootcss.com/jquery/3.1.0/jquery.js"></script>
<script src="http://cdn.bootcss.com/jquery-cookie/1.4.1/jquery.cookie.js"></script>
<!-- <script src="https://cdn.bootcss.com/jquery-cookie/1.4.1/jquery.cookie.min.js"></script>-->
</head>
<body>
<input id="phonenum" type="text" value="18518181818"/>
<input id="second" type="button" value="免费获取验证码" />
</body>
<script>
//发送验证码时添加cookie
function addCookie(name,value,expiresHours){ 
//判断是否设置过期时间,0代表关闭浏览器时失效
if(expiresHours>0){ 
var date=new Date(); 
date.setTime(date.getTime()+expiresHours*1000); 
$.cookie(name, escape(value), {expires: date});
}else{
$.cookie(name, escape(value));
}
} 
//修改cookie的值
function editCookie(name,value,expiresHours){ 
if(expiresHours>0){ 
var date=new Date(); 
date.setTime(date.getTime()+expiresHours*1000); //单位是毫秒
$.cookie(name, escape(value), {expires: date});
} else{
$.cookie(name, escape(value));
}
} 
//根据名字获取cookie的值
function getCookieValue(name){ 
return $.cookie(name);
}
$(function(){
$("#second").click(function (){
sendCode($("#second"));
});
v = getCookieValue("secondsremained");//获取cookie值
if(v>0){
settime($("#second"));//开始倒计时
}
})
//发送验证码
function sendCode(obj){
var phonenum = $("#phonenum").val();
var result = isPhoneNum();
if(result){
// doPostBack('${base}/login/getCode.htm',backFunc1,{"phonenum":phonenum});
addCookie("secondsremained",60,60);//添加cookie记录,有效时间60s
settime(obj);//开始倒计时
}
}
//开始倒计时
var countdown;
function settime(obj) { 
countdown=getCookieValue("secondsremained");
if (countdown == 0) { 
obj.removeAttr("disabled"); 
obj.val("免费获取验证码"); 
return;
} else { 
obj.attr("disabled", true); 
obj.val("重新发送(" + countdown + ")"); 
countdown--;
editCookie("secondsremained",countdown,countdown+1);
} 
setTimeout(function() { settime(obj) },1000) //每1000毫秒执行一次
} 
//校验手机号是否合法
function isPhoneNum(){
var phonenum = $("#phonenum").val();
var myreg = /^(((13[0-9]{1})|(15[0-9]{1})|(18[0-9]{1}))+\d{8})$/; 
if(!myreg.test(phonenum)){ 
alert('请输入有效的手机号码！'); 
return false; 
}else{
return true;
}
}
</script>
</html>