CODEWITHSUNDEEP
node.js
Babr
Babr

Reputation: 2081

Node.js UnhandledPromiseRejectionWarning: Error: Can't set headers after they are sent

I'm new to node.js and want to send out dataof User and Match in a single response by querying mongodb twice . 

 router.get('/preview/',  checkAuth, (req, res)=> {
    const errors = {};
    const match = {}
    User.findOne({_id: req.user.id})
    .then(user => {
      if (!user) {
        return res.status(404).json({errors: 'Could not find a user' });
      }

      Match.findOne({ user: req.user.id }).then(m => { 
        console.log('match found!');
        match = m;
      }).catch(err=> res.status(404).json(err));  // <-error occures here

      res.status(200).json({user, match});
    })
    .catch(err=> res.status(404).json(err));

  });

But I get this error:

(node:8056) UnhandledPromiseRejectionWarning: Error: Can't set headers after they are sent.

How can I fix it?

Upvotes: 0

Views: 220

Answers (1)

Niral Munjariya
Niral Munjariya

Reputation: 1371

Please have a look at the comments added in your code.

router.get('/preview/',  checkAuth, (req, res)=> {
    const errors = {};
    const match = {}
    User.findOne({_id: req.user.id})
    .then(user => {
      if (!user) {
        return res.status(404).json({errors: 'Could not find a user' });
      }

      Match.findOne({ user: req.user.id }).then(m => { 
        console.log('match found!');
        match = m;
      }).catch(err=> res.status(404).json(err));  // <-error occures here because you sent the response if error occurs

      res.status(200).json({user, match}); // this will be executed even if there is an error so it will again try to send the response
    })
    .catch(err=> res.status(404).json(err));

  });

Improved code:

router.get('/preview/', checkAuth, (req, res) => {
  const errors = {};
  User.findOne({ _id: req.user.id })
    .then((user) => {
      if (!user) {
        return res.status(404).json({ errors: 'Could not find a user' });
      }
      Match.findOne({ user: req.user.id })
        .then((m) => {
          console.log('match found!');
          res.status(200).json({ user, m }); // send the success response when the match found
        })
        .catch((err) => res.status(404).json(err)); // send the error response when erro thrown
    })
    .catch((err) => res.status(404).json(err));
});

Upvotes: 2

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