Question

我是Node的新手。我试图绕过这个错误，我不明白为什么。我看过它的几个帖子，但它们都是不同的情况，没有一个与我相匹配。所以感谢帮助。从我在其他帖子中看到的情况来看，这是一个帖子中的大多数情况，我的确是一个得到的错误。

 GET /posts/56f2a808653270ff11f7ddb2 304 30.391 ms - -
 _http_outgoing.js:344
     throw new Error('Can\'t set headers after they are sent.');
     ^

 Error: Can't set headers after they are sent.
     at ServerResponse.OutgoingMessage.setHeader (_http_outgoing.js:344:11)
     at ServerResponse.header (/Users/me/nodyhead/node_modules/express/lib/response.js:718:10)
     at ServerResponse.json (/Users/me/nodyhead/node_modules/express/lib/response.js:246:10)
     at /Users/me/nodyhead/routes/index.js:50:13
     at next (/Users/me/nodyhead/node_modules/mongoose/lib/model.js:2491:5)
     at EventEmitter.<anonymous> (/Users/me/nodyhead/node_modules/mongoose/lib/model.js:2621:5)
     at EventEmitter.<anonymous> (/Users/me/nodyhead/node_modules/mpromise/lib/promise.js:180:45)
     at emitThree (events.js:97:13)
     at EventEmitter.emit (events.js:175:7)
     at Promise.safeEmit (/Users/me/nodyhead/node_modules/mpromise/lib/promise.js:83:21)
     at Promise.fulfill (/Users/me/nodyhead/node_modules/mpromise/lib/promise.js:104:24)
     at Promise.resolve (/Users/me/nodyhead/node_modules/mongoose/lib/promise.js:142:23)
     at next (/Users/me/nodyhead/node_modules/mongoose/lib/model.js:2687:15)
     at /Users/me/nodyhead/node_modules/kareem/index.js:177:19
     at /Users/me/nodyhead/node_modules/kareem/index.js:109:16
     at nextTickCallbackWith0Args (node.js:420:9) [nodemon] app crashed - waiting for file changes before starting...

这是我抱怨的三个功能

router.get('/posts', function(req, res, next) {
    Post.find(function(err, posts) {
        if (err) { return next(err); }

        res.json(posts);
    });
});


router.param('post', function(req, res, next, id) {
    var query = Post.findById(id);

    query.exec(function(err, post) {
        if (err) { return next(err); }
        if (!post) { return next(new Error('can\'t find post')); }

        req.post = post;
        return next();
    });
});

router.get('/posts/:post', function(req, res) {
    req.post.populate('comments', function(err, post) {
        if (err) { return next(err); }

        res.json(post);
    });

    res.json(req.post);
});

Answer 1

嗯，问题是你两次调用res.json（）。有关详细信息，请参阅本主题Error: Can't set headers after they are sent to the client的答案

Answer 2

在GET posts/:post（您的上一个处理程序）中删除其中一条res.json(obj)行。这里的要点是你的响应是两次：一次是在回调执行之前，一次是在数据库访问之后。只保留其中一个。

Node.js，错误344，在设置后无法设置标头

2 个答案: