blocks|key|747092|text|最明显的方法确实是将它们封装在promise中以启动您的promise链(+User.findOne位于第一个then-block中)-这样您当前的错误处理程序就可以很好地捕获它们。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|747093|entityMap^0|12|C|1J|4|0^^$0|@$1|2|3|4|5|6|7|H|8|@$9|I|A|J|B|C]|$9|K|A|L|B|C]]|D|@]|E|$]]|$1|F|3|-4|5|6|7|M|8|@]|D|@]|E|$]]]|G|$]]

The obvious way would indeed be to encapsulate them in a promise to start your promise chain (with the <code>User.findOne</code> being inside the first <code>then</code>-block) - that way your current error handler catches them just fine.

blocks|key|747107|text|您可以将您的函数包装在promise中，并有效地处理它|type|unstyled|depth|inlineStyleRanges|entityRanges|data|747108|function+getRes(){++
++++return+new+Promise(function(resolve,+reject){
++++++++const+username+=+req.body.username;
++++++++const+password+=+req.body.password;

++++++++if+(!username)+{
++++++++++reject(new+Error('Missing+username'));
++++++++}

++++++++if+(!password)+{
++++++++++reject(new+Error('Missing+password'));
++++++++}

++++++++resolve(User.findOne({+username,+password+}));
++++});
}


getRes().then(function(result){
++++res.json(result);
}).catch(function(err){
++++res.json(err);
})|code-block|syntax|javascript|747109|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

you can wrap your functions in a promise and handle it efficiently

<pre><code>function getRes(){ 
 return new Promise(function(resolve, reject){
 const username = req.body.username;
 const password = req.body.password;

 if (!username) {
 reject(new Error('Missing username'));
 }

 if (!password) {
 reject(new Error('Missing password'));
 }

 resolve(User.findOne({ username, password }));
 });
}


getRes().then(function(result){
 res.json(result);
}).catch(function(err){
 res.json(err);
})
</code></pre>

blocks|key|747138|text|在您的第一个解决方案中，抛出的错误将不会被处理，因为您将它们抛出promise链之外，并且没有try/catch块。在第二个解决方案中，您可能会得到cannot+send+headers+after+they+sent错误，因为响应可以发送两次(缺少username和缺少password+)。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|747139|因此，这里可能的解决方案之一是创建一个promise链(使用Promise.resolve())并在此处验证参数：|747140|function+validateParams()+{
++const+username+=+req.body.username;
++const+password+=+req.body.password;

++if+(!username)+{
++++throw+new+Error('Missing+username');
++}
++if+(!password)+{
++++throw+new+Error('Missing+password');
++}
++return+{+username,+password+};
}

Promise
++.resolve()
++.then(validateParams)
++.then(filter+=>+User.findOne(filter))
++.then(user+=>+res.json(user))
++.catch(err+=>+res.json(err));|code-block|syntax|javascript|747141|entityMap^0|1B|9|22|Z|3H|8|3S|8|0|U|H|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@$9|P|A|Q|B|C]|$9|R|A|S|B|C]|$9|T|A|U|B|C]|$9|V|A|W|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|X|8|@$9|Y|A|Z|B|C]]|D|@]|E|$]]|$1|H|3|I|5|J|7|10|8|@]|D|@]|E|$K|L]]|$1|M|3|-4|5|6|7|11|8|@]|D|@]|E|$]]]|N|$]]

In your first solution, the thrown errors won't be handled, because you throw them outside of promise chain and without <code>try/catch</code> block. In your second solution you can get <code>cannot send headers after they sent</code> error, because the response can be sent twice (<code>username</code> is missing and <code>password</code> is missing).

So the one of the possible solutions here, is to create a promise chain (using <code>Promise.resolve()</code>) and validate parameters here:

<pre><code>function validateParams() {
 const username = req.body.username;
 const password = req.body.password;

 if (!username) {
 throw new Error('Missing username');
 }
 if (!password) {
 throw new Error('Missing password');
 }
 return { username, password };
}

Promise
 .resolve()
 .then(validateParams)
 .then(filter =&gt; User.findOne(filter))
 .then(user =&gt; res.json(user))
 .catch(err =&gt; res.json(err));
</code></pre>

blocks|key|747177|text|我以@alexmac为例，使用es6异步特性：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|747178|function+validateParams()+{
++const+username+=+req.body.username;
++const+password+=+req.body.password;

++if+(!username)+{
++++throw+new+Error('Missing+username');
++}
++if+(!password)+{
++++throw+new+Error('Missing+password');
++}
++return+{+username,+password+};
}

async+function+resolver()+{
++++try+{
++++++++await+resolve()
++++++++let+filter+=+validateParams()
++++++++let+user+=+await+User.findOne(filter)
++++++++await+res.json(user)
++++}+catch+(e)+{
++++++++await+res.json(e)
++++}
+}|code-block|syntax|javascript|747179|如果使用if而不是throw，看起来会更美观|offset|length|style|CODE|747180|async+function(req,+res)+{
++++const+password+=+req.body.password
++++const+username+=+req.body.username
++++let+c+=+!password+?+'missing+password'+:+
++++++++++++++++!username+?+'missing+username'+:+null
++++if+(!c)+{
+++++++c+=+await+User.findOne({+username,+password+})
++++}
++++await+res.json(c)
}|747181|entityMap^0|0|0|4|2|9|5|0|0^^$0|@$1|2|3|4|5|6|7|Q|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|R|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|S|8|@$I|T|J|U|K|L]|$I|V|J|W|K|L]]|9|@]|A|$]]|$1|M|3|N|5|D|7|X|8|@]|9|@]|A|$E|F]]|$1|O|3|-4|5|6|7|Y|8|@]|9|@]|A|$]]]|P|$]]

I'm taking the example from @alexmac and use es6 async feature:

<pre><code>function validateParams() {
 const username = req.body.username;
 const password = req.body.password;

 if (!username) {
 throw new Error('Missing username');
 }
 if (!password) {
 throw new Error('Missing password');
 }
 return { username, password };
}

async function resolver() {
 try {
 await resolve()
 let filter = validateParams()
 let user = await User.findOne(filter)
 await res.json(user)
 } catch (e) {
 await res.json(e)
 }
 }
</code></pre>

and that would look more elegant by using an <code>if</code> instead of a <code>throw</code>:

<pre><code>async function(req, res) {
 const password = req.body.password
 const username = req.body.username
 let c = !password ? 'missing password' : 
 !username ? 'missing username' : null
 if (!c) {
 c = await User.findOne({ username, password })
 }
 await res.json(c)
}
</code></pre>

I have a function to log in a user which should return JSON.

<pre><code>const username = req.body.username;
const password = req.body.password;

if (!username) {
 throw new Error('Missing username');
}

if (!password) {
 throw new Error('Missing password');
}

User.findOne({ username, password }).then(user =&gt; {
 res.json({ user });
}).catch(err =&gt; {
 res.json({ err });
});
</code></pre>

but then the errors for missing username or missing password are not returned in JSON.

I could change it to

<pre><code>const username = req.body.username;
const password = req.body.password;

if (!username) {
 res.json({ err: 'Missing username' });
}

if (!password) {
 res.json({ err: 'Missing password' });
}

User.findOne({ username, password }).then(user =&gt; {
 res.json({ user });
}).catch(err =&gt; {
 res.json({ err });
});
</code></pre>

but it seems a little redundant.

Is the correct way to do it to encapsulate it in a promise?

Throw errors outside of promise

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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我有一个登录用户的函数，它应该返回JSON。const username = req.body.username;const password = req.body.password;if (!username) {  throw new Error('Missing username');}if (!password...

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