javascript - 等待 promise 解决并在它解决时做其他事情

Question

我有一个函数做两件事，某件事需要 I/O 时间，我想第二件事返回它，但我希望另一件事在这段时间内处理并快速发送，即使第一件事还没有完成

getuser(x){
    let username = getUsernameDB(x.id);//takes time to get data it is an async function

    sendMessage(x.id,() => {//send message with callback function when it is recived
       sendMessage(username);//must wait for getUsernameFromDatabase
    });

}

async getUsernameDB(id){
return await this.dataaccess.getUsernameByUserId(id);//this returns new Promise
}

所以我主要想做一个 promise ，执行其他代码然后在这里等待这个 promise 解决然后继续。

Answer 1

.then 应该放在第一个 sendmessage 调用之后。这将使 promise 函数与 sendmessage 并行运行，然后在发送第二条消息之前等待 resolve

getuser(x){
    let username = getUsernameDB(x.id);//takes time to get data it is an async function

    sendMessage(x.id,() => {//send message with callback function when it is recived
        username.then((usernameVar) => {
            sendMessage(usernameVar);//usernameVar is carring the value now
    })

    });

}

async getUsernameDB(id){
return await this.dataaccess.getUsernameByUserId(id);//this returns new Promise
}