entityMap|blocks|key|ehdk3|text|不能在调用res.end之后发送响应，这是在调用res.send函数时由express在内部完成的|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|akek4|在本例中，只需在出现错误时添加return|ajmh5|if+(err)+{
++++return+res.status(400).send(err);
}|code-block|syntax|javascript|9qnqv^0|5|7|O|8|0|F|6|0|0^^$0|$]|1|@$2|3|4|5|6|7|8|O|9|@$A|P|B|Q|C|D]|$A|R|B|S|C|D]]|E|@]|F|$]]|$2|G|4|H|6|7|8|T|9|@$A|U|B|V|C|D]]|E|@]|F|$]]|$2|I|4|J|6|K|8|W|9|@]|E|@]|F|$L|M]]|$2|N|4|-4|6|7|8|X|9|@]|E|@]|F|$]]]]

You can't send response after <code>res.end</code> is called, which is done internally by express when you call <code>res.send</code> function

In your case just add <code>return</code> when there's an error

<pre><code>if (err) {
 return res.status(400).send(err);
}
</code></pre>

entityMap|blocks|key|85uv1|text|因为在发送状态的错误情况下不会返回，所以下面的代码只是在之后执行。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3vkr0|你需要写：return+res.status(400).send(err);或者直接使用if+else|offset|length|style|CODE|cbaa6^0|0|5|X|18|7|0^^$0|$]|1|@$2|3|4|5|6|7|8|J|9|@]|A|@]|B|$]]|$2|C|4|D|6|7|8|K|9|@$E|L|F|M|G|H]|$E|N|F|O|G|H]]|A|@]|B|$]]|$2|I|4|-4|6|7|8|P|9|@]|A|@]|B|$]]]]

Because you don't return in that error case where you send status, so that code bellow just executes after anyway.

You need to write: <code>return res.status(400).send(err);</code>
or just use <code>if else</code>

entityMap|blocks|key|2uqed|text|你关于res.send()破坏的假设是不正确的，只有当你return的时候它才会这样做。在发生错误的情况下调用res.send()上的return，这样它就不会继续执行。如果你得到一个错误，它会将状态设置为400+(在标题中)，然后主体中的错误，但因为它不返回它，然后尝试将状态设置为200+(在标题中)，从而导致您看到的错误。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|agjd|//+save+the+team+and+check+for+errors
team.save(function+(err)+{
++++if+(err)+{
++++++++//+return+here+so+that+it+will+not+continue!
++++++++return+res.status(400).send(err);
++++}

++++//+return+here+if+there+is+no+error!
++++return+res.status(200).json({
++++++++message:+'Team+successfully+created',
++++++++team:+team
++++});
});|code-block|syntax|javascript|742bc|Express使用function(req,+res,+next)将中间件链接在一起，并且可以在多个中间件中通过res.send()返回结果。链中的下一个中间件在您成功执行return+next()时被调用，因此，例如，如果您希望在成功时在另一个中间件中返回额外的数据，则不会执行return+res.send()，而是在res.send()之后调用return+next()。|56u8q^0|3|A|S|6|1J|A|1V|6|0|0|9|O|1K|A|2E|D|3W|H|4H|A|4V|D|0^^$0|$]|1|@$2|3|4|5|6|7|8|O|9|@$A|P|B|Q|C|D]|$A|R|B|S|C|D]|$A|T|B|U|C|D]|$A|V|B|W|C|D]]|E|@]|F|$]]|$2|G|4|H|6|I|8|X|9|@]|E|@]|F|$J|K]]|$2|L|4|M|6|7|8|Y|9|@$A|Z|B|10|C|D]|$A|11|B|12|C|D]|$A|13|B|14|C|D]|$A|15|B|16|C|D]|$A|17|B|18|C|D]|$A|19|B|1A|C|D]]|E|@]|F|$]]|$2|N|4|-4|6|7|8|1B|9|@]|E|@]|F|$]]]]

entityMap|blocks|key|77tfj|text|您得到的错误是因为代码行|type|unstyled|depth|inlineStyleRanges|entityRanges|data|8mndv|++res.status(200).json({
++++message:+'Team+successfully+created',
++++team:+team
});|code-block|syntax|javascript|4njpf|无论是否发生错误都会被调用。在出现错误的情况下，响应报头已经在此代码中由express发送|3s98j|if+(err)+{
++++res.status(400).send(err);
}|88stk|因此，当express尝试下面的代码时，它会得到您所表达的错误。答案是使用Rami+Jarrar提供的答案|cq0r8|+//+save+the+team+and+check+for+errors
team.save(function+(err)+{
++++if+(err)+{
++++++++res.status(400).send(err);
++++}

++++res.status(200).json({
++++++++message:+'Team+successfully+created',
++++++++team:+team
++++});
});|4k904^0|0|0|0|0|0|0^^$0|$]|1|@$2|3|4|5|6|7|8|Q|9|@]|A|@]|B|$]]|$2|C|4|D|6|E|8|R|9|@]|A|@]|B|$F|G]]|$2|H|4|I|6|7|8|S|9|@]|A|@]|B|$]]|$2|J|4|K|6|E|8|T|9|@]|A|@]|B|$F|G]]|$2|L|4|M|6|7|8|U|9|@]|A|@]|B|$]]|$2|N|4|O|6|E|8|V|9|@]|A|@]|B|$F|G]]|$2|P|4|-4|6|7|8|W|9|@]|A|@]|B|$]]]]

The error that you are getting is because the line of code 

<pre><code> res.status(200).json({
 message: 'Team successfully created',
 team: team
});
</code></pre>

is being called whether it gets error or not . In case of the error the response header is already being sent in this code by the express

<pre><code>if (err) {
 res.status(400).send(err);
}
</code></pre>

So when the express tries the code below it gets the error that you expressed . The answer is to use the answer provided by Rami Jarrar

<pre><code> // save the team and check for errors
team.save(function (err) {
 if (err) {
 res.status(400).send(err);
 }

 res.status(200).json({
 message: 'Team successfully created',
 team: team
 });
});
</code></pre>

entityMap|blocks|key|8gai4|text|请尝试这个：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|dauvv|team.save(function+(err)+{
++++if+(err)+{
++++++++return+res.status(400).send(err);+//+here+i+have+added+a+return
++++}

++++res.status(200).json({
++++++++message:+'Team+successfully+created',
++++++++team:+team
++++});
}|code-block|syntax|javascript|1gric|问题是，当我们将响应发送到客户端时，tcp连接将关闭，并且再次在相同的响应对象上发送数据将抛出一个错误，这是您在当前代码中得到的错误。|dbla2^0|0|0|0^^$0|$]|1|@$2|3|4|5|6|7|8|K|9|@]|A|@]|B|$]]|$2|C|4|D|6|E|8|L|9|@]|A|@]|B|$F|G]]|$2|H|4|I|6|7|8|M|9|@]|A|@]|B|$]]|$2|J|4|-4|6|7|8|N|9|@]|A|@]|B|$]]]]

Please try with this:

<pre><code>team.save(function (err) {
 if (err) {
 return res.status(400).send(err); // here i have added a return
 }

 res.status(200).json({
 message: 'Team successfully created',
 team: team
 });
}
</code></pre>

The problem is when we send the response to client the tcp connection will be closed and sending data on the same response object again will throw an error which you are getting in current code.

I have an issue with the below code. When an error is hit, the if statement is been hit and res.send is been called. However, the code then continues onto the res.json call below. This results in the headers error.

Is using an else statement the only correct way to do this? I would assume that calling res.send would break from the function.

<pre><code>exports.new = function (req, res) {
 let team = new Team();
 team.name = req.body.name;
 team.description = req.body.description;
 team.members = [];

 // save the team and check for errors
 team.save(function (err) {
 if (err) {
 res.status(400).send(err);
 }

 res.status(200).json({
 message: 'Team successfully created',
 team: team
 });
 });
};
</code></pre>

I have also tried using req, res, next as the function parameters and using the following method:

<pre><code>if (err) {
 res.status(400);
 next(err);
}

res.status(200).json({
 message: 'Team successfully created',
 team: team
});
</code></pre>

Whilst this doesn't throw an error, it still proceeds to call the final res.status.json (resulting in a 200, not a 400 response)

Error: Can't set headers after they are sent - Correctly handling an error in an express controller

中间件

 我对下面的代码有一个问题。当命中错误时，将命中if语句并调用res.send。但是，代码随后继续执行下面的res.json调用。这会导致报头错误。 使用else语句是唯一正确的方法吗？我假设调用res.send会中断函数。 exports.new = function (req, res) {    let team...

问错误:无法在发送后设置标头-正确处理express控制器中的错误
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