function get_cookie(key) {

        var arr, reg = new RegExp("(^| )" + key + "=([^;]*)(;|$)");

        arr = document.cookie.match(reg)

        return arr ? arr[2] : null

    }

    function set_cookie(key, value, day, domain) {

        var exdatestr = ''

        domain = domain || location.hostname

        if (day) {

            var date = new Date()

            date.setDate(date.getDate() + day)

            exdatestr = ';expires=' + date.toGMTString()

        }

        var cookie = key + '=' + value + exdatestr + ';path=/;domain=' + domain

        document.cookie = cookie

        console.log('document.cookie', cookie);

    }

//--------------------------------------------------------------

// 调用

set_cookie('once', '123', 24)

get_cookie('once')