promise

 let checkLogin=()=>{
    return new Promise ((resolve,reject)=>{
        let flag =document.cookie.indexOf('userId')>-1>true:false;
        if(flag){
            resolve({
                status:0,
                result:true
            })
        }else{
            reject("error")
        }
    }
    )
}

checkLogin().then((res)=>{
    if(res.status ===0){
        return 'login Success!'
    }
}).catch((error)=>{
    return error
})