存一个有效期为7天的cookie，key = nickname, val = Ace

       function setCookie(key, val, expires) {//设置cookie，封装，kay，cal键值对，加过期时间
        let now = new Date()
        now.setDate(now.getDate() + expires)
        document.cookie = `${key}=${val};expires=${now.toUTCString()}`//模板字符串
    }

    function removeCookie(key) {//关闭cookie 传一个参数key
        setCookie(key, null, -1)
    }

    setCookie('count', 22, 7)
    // setCookie('age1', 33, 2)
    removeCookie('age1')
    console.log(document.cookie);

    function getCookie(key) {//分割键值对
        let obj = {}
        let cookies = document.cookie.split('; ')
        cookies.forEach(r => {
            let kv = r.split('=')
            let key = kv[0]
            let val = kv[1]
            obj[key] = val
        })
        if (key) return obj[key]
        return obj
    }

    console.log(getCookie());
    console.log(getCookie('age'));
    console.log(getCookie('username'));