CODEWITHSUNDEEP
javascriptnode.jsexpress
user6885115
user6885115

Reputation:

Node Express chaining functions returns UnhandledPromiseRejectionWarning

I'm breaking up a Node Endpoint so that 2 things happen

  1. Checks if User Exists
  2. Adds user to the database

controller.js

exports.signup = (req, res) => {
  methods.checkUser('email', req.body.email)
    .then(methods.addUser(req.body.email, req.body.password))
    .then(() => {
      res.send('added');
    })
    .catch((err) => {
      console.log(err);
      res.status(403).send(err);
    });
};

methods.js

exports.checkUser = (key, val) => {
  return new Promise((resolve, reject) => {
    db.query('SELECT * FROM ?? WHERE ?? = ?', ['users', key, val], (err, result) => {
      if (result) {
        resolve(result);
      } else {
        reject(err);
      }

    });
  });
};

exports.addUser = (email, password) => {
  return new Promise((resolve, reject) => {
    if (email === '[email protected]') {
      resolve(true);
    } else {
      console.log('rejecting');
      reject(email);
    }
  });
};

addUser() currently just checks if the email === [email protected] to test out the Promise chain.

So the endpoint returns added in Postman

But Terminal shows the following

rejecting
(node:71904) UnhandledPromiseRejectionWarning: Unhandled promise rejection (rejection id: 1): [email protected]
(node:71904) [DEP0018] DeprecationWarning: Unhandled promise rejections are deprecated. In the future, promise rejections that are not handled will terminate the Node.js process with a non-zero exit code.

Typically I would have wrote it like this.

exports.signup = (req, res) => {
  methods.checkUser('email', req.body.email)
    .then(() => {
      methods.addUser(req.body.email, req.body.password)
        .then(() => {
          res.send('added');
        })
        .catch((err) => {
          res.status(403).send(err);
        })
    })
    .catch((err) => {
      console.log(err);
      res.status(403).send(err);
    });
};

I want to take a cleaner approach but need help

Upvotes: 0

Views: 72

Answers (1)

loretoparisi
loretoparisi

Reputation: 16311

This is a correct way to write the Promise chain:

exports.signup = (req, res) => {
    methods.checkUser('email', req.body.email)
      .then(() => methods.addUser(req.body.email, req.body.password) )
      .then(() => res.send('added') )
      .catch((err) => {
        console.log(err);
        res.status(403).send(err);
      });
  };

so in case of a reject in the chain, like in the case of the [email protected] input in the example, the rejection will be handled by the last catch.

Upvotes: 1

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