如何从 Promise<User> 获取用户名？
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【中文标题】如何从 Promise<User> 获取用户名？【英文标题】：How to obtain username from Promise<User>? 【发布时间】：2020-11-22 22:57:52 【问题描述】：我正在使用 Discord.js，但我不知道如何从 Promise 中获取价值。这是一些上下文：
///File: commands/mail.js///
module.exports =
name: 'mail',
description: 'A system of collecting, sending, and receiving mail',
async execute(client,message, args)
const fs = require('fs');
...
...
switch(args[0])
...
case "check":
...
var name;
var val;
/* [object Promise]--> */ var out = client.users.fetch(recipient.senders[i]);
client.users.fetch(recipient.senders[i]).then((name)=>
console.log("name.username(inside): "+name.username);
val = name.username;
return (name);
);
console.log("name(outside): ",name);
console.log("out: ",out);
console.log("out.username: ",out.username);
console.log("val: ",val);
/* next line will get an error saying name.username is undefined */
//console.log("name.username(outside): "+name.username);
...
我得到了输出：
name(outside): undefined
out: Promise
User
id: '1456051390970320640',
bot: false,
username: 'Sir_Ross',
discriminator: '3871',
avatar: 'a956037b05108e4971b93f3ffde97b6c',
lastMessageID: '739552900342349856',
lastMessageChannelID: '739150130339340342',
flags: UserFlags bitfield: 0
val: undefined
out.username: undefined
name.username(inside): Sir_Ross
我的问题是我显然可以获取我的用户名并将其打印到控制台，但我无法将其从 Promise 中取出。如何从 Promise 中获取价值，以便我可以在其他地方使用它？
完整代码：
module.exports =
name: 'mail',
description: 'A system of collecting, sending, and receiving mail',
async execute(client,message, args)
const fs = require('fs');
var path;
if(!args.length)
//No Arguments
return 0;
switch(args[0])
case "send":
// Send Mail
if(args.length<3)
message.reply('Invalid Arguments: !mail send <recipient_id> <message>');
else
letter = "";
spaces = 0;
for(i = 0; i<message.content.length;i++)
if(spaces<3)
if(message.content[i]===' ')
spaces++;
continue;
else
letter+=message.content[i];
const fs = require('fs');
path = 'mail/';
path+=args[1].substring(3,21);
sender = message.author.id;
path+='.json';
console.log(path);
if(!fs.existsSync(path))
user =
user_id: args[1].substring(3,21),
//username: message.author.username,
mailbox: [letter],
senders: [sender],
//status: 0 ,
status: ['0'],
;
data = JSON.stringify(user);
fs.writeFileSync(path,data);
else
var recipient;
fs.readFile(path,(err,data) =>
if(err) throw err;
recipient=JSON.parse(data);
//console.log(recipient);
recipient.mailbox.push(letter);
recipient.senders.push(message.author.id);
recipient.status.push('0');
console.log(recipient);
fs.writeFileSync(path,JSON.stringify(recipient));
);
break;
case "check":
// Check Inbox
const fs = require('fs');
path = 'mail/';
path+=message.author.id;
// sender = message.author.id;
path+='.json';
if(!fs.existsSync(path))
message.reply("Mailbox does not yet exist! You need to receive mail first!");
return;
//break;
else
var recipient;
fs.readFile(path,(err,data) =>
if(err) throw err;
recipient=JSON.parse(data);
if(!recipient.senders.length)
message.reply("Mailbox is empty!");
return;
//break;
else
outText = "";
for(i = 0; i<recipient.senders.length;i++)
if(recipient.status[i]==='0')outText+="**";
outText+=i+1;
outText+=". ";
//console.log("Promise: ",client.users.fetch(recipient.senders[i]));
var name;
var val;
var out = client.users.fetch(recipient.senders[i]);
client.users.fetch(recipient.senders[i]).then((name)=>
console.log("name.username(inside): "+name.username);
val = name.username;
return (name);
);
console.log("name(outside): ",name);
console.log("out: ",out);
console.log("out.username: ",out.username);
console.log("val: ",val);
/* name.username is undefined */
//console.log("name.username(outside): "+name.username);
// esc = returnVal();
outText+=val;
if(recipient.status[i]==='0')outText+="**";
outText+='\n';
message.reply(outText);
);
break;
case "read":
// Read Mail
break;
case "delete":
// Delete Mail
break;
case "markRead":
// Mark a Message as Read
break;
case "markUnread":
// Mark a Message as Unread
break;
case "forward":
// Forward a message
break;
,
;
【问题讨论】：
只要await 它，因为你在async 函数中？
@Bergi 问题是你需要在async 函数中创建一个await，它说我不再在async 函数中
那么请分享您的实际代码，因为从您发布的内容来看，您的问题发生在 async execute(client,message, args) 方法中。
啊，你在 fs.readFile 回调中。不要那样做 - promisify the readFile method 并写 const data = await readFileAsync(path); const recipient = JSON.parse(data); … 这样你的 fetch 调用仍然在 execute 内。
@Bergi 我搞定了，非常感谢！
【参考方案1】：
正如@Bergi 在他的评论中所说，我需要将我的代码从fs.readFile 回调中取出。
为此，我修改了我的代码：
var recipient;
fs.readFile(path,(err,data) =>
if(err) throw err;
recipient=JSON.parse(data);
...
进入
function readFileAsync(path)
return new Promise(function(resolve, reject)
fs.readFile(path, function(err,data)
if(err!==null)reject(err);
else resolve(data);
);
);
const data = await readFileAsync(path); const recipient = JSON.parse(data);
他的链接很有用（特别是3. Node style callback ("nodeback")部分）：How do I convert an existing callback API to promises?
【讨论】：
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