JS获取验证码后倒计时不受刷新及关闭影响

HTML部分

<input type="button" id="code_btn" value="获取验证码">   

JS部分

//获取验证码
$(function() {
    $("#code_btn").on("tap", function() {
        if(!rex.test($("#tel").val())) {
            tip("请输入正确手机号");
            return false;
        }
        $.ajax({
            async: false,
            cache: false,
            type: 'POST',
            url: forgetConfirmUrl, // 请求的action路径
            data: {
                phone: $("#tel").val()
            },
            dataType: "json",
            success: function(data) {
                console.log(data);
                if(data.error_code == 0) {
                    tip("发送成功");
                } else if(data.error_code == 1) {
                    tip("用户未注册");
                } else if(data.error_code == 2) {
                    tip("手机号值为空");
                } else if(data.error_code == 3) {
                    tip("手机号格式不正确");
                } else {
                    tip("网络异常");
                }
            }
        });
        addCookie("secondsremained", 60, 60); //添加cookie记录,有效时间60s
        settime($("#code_btn")); //开始倒计时
    })
    var v = getCookieValue("secondsremained") ? getCookieValue("secondsremained") : 0;//获取cookie值
    if(v > 0) {
        settime($("#code_btn")); //开始倒计时
    }
})
//发送验证码时添加cookie
function addCookie(name, value, expiresHours) {
    var cookieString = name + "=" + escape(value);
    //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);
        cookieString = cookieString + ";expires=" + date.toUTCString();
    }
    document.cookie = cookieString;
}
//修改cookie的值
function editCookie(name, value, expiresHours) {
    var cookieString = name + "=" + escape(value);
    if(expiresHours > 0) {
        var date = new Date();
        date.setTime(date.getTime() + expiresHours * 1000); //单位是毫秒
        cookieString = cookieString + ";expires=" + date.toGMTString();
    }
    document.cookie = cookieString;
}
//根据名字获取cookie的值
function getCookieValue(name) {
    var strCookie = document.cookie;
    var arrCookie = strCookie.split("; ");
    for(var i = 0; i < arrCookie.length; i++) {
        var arr = arrCookie[i].split("=");
        if(arr[0] == name) {
            return unescape(arr[1]);
            break;
        }
    }
}
//开始倒计时
var countdown;
function settime(obj) {
    countdown = getCookieValue("secondsremained");
    var tim = setInterval(function() {
            countdown--;
            obj.attr("disabled", true);
            obj.attr("value", "重新发送(" + countdown + ")");
            if(countdown <= 0 ) {
                clearInterval(tim);
                $(obj).removeAttr("disabled");
                $(obj).attr("value", "请输入验证码");
            }
            editCookie("secondsremained", countdown, countdown + 1);
        }, 1000) //每1000毫秒执行一次
}