系统登录时，选中记录帐号、密码，则会保存在COOKIE中；后续有效期内访问输入帐号，则自动带出密码

//设置Cookie
function setCookie(name, value, expdays){
    let expdate = new Date();
    //设置Cookie过期日期
    expdate.setDate(expdate.getDate() + expdays);
    //添加Cookie
    document.cookie = name + "=" + escape(value) + ";expires=" + expdate.toUTCString();
}

//获取Cookie
function getCookie(name){
    if(document.cookie.length>0){
        //获取name在Cookie中起止位置
        let start = document.cookie.indexOf(name + "=");

        if(start != -1){
            start = start + name.length + 1;
            //获取value的终止位置
            let end = document.cookie.indexOf(";", start);
            if(end == -1){
                end = document.cookie.length
            };

            //截获cookie的value值,并返回
            return unescape(document.cookie.substring(start, end));
        }
    }
    return "" ;
}

//清除Cookie
function delCookie(name){
    setCookie(name, "", -1);
}