Error in Promise Not sending any error in response object in NodeJS/Express/Mongoose

Question

I am trying to convert old mongoose promise code to Native ES6 Promise. I am getting all the errors thrown in catch and I can log it in console but when I try to pass it to response object I get empty object. Following is my code

module.exports.login = function(req, res) {

    var userPromise = User.findOne({email:req.body.email}).exec();

    userPromise.then(function(user) {
        if(!user){
            throw new Error("step 1 failed!");
        }
    })
    .then(function(user) {
        if(!user.comparePassword(req.body.password)){
            throw new Error("step 2 failed!");
        }else {
            return res.json({token: jwt.sign({email:user.email, name:user.name, _id: user._id}, 'SOMETOKEN')});

        }
    })
    .catch(function(err) {
        console.log('Error: '+err);
        return res.status(401).send(err);       

    });
};

Please do let me know if I am on a right path or am I doing some mistake over here. Thanks in advance.

Answer 1

An Error instance is an object, and Express will (AFAIK) use code similar to this:

res.status(401).send(JSON.stringify(err))

The result of JSON.stringify(err) is {} because its main properties ( name , message and stack ) are not enumerable.

I'm not sure what exactly you want to return to the user, but it's common to send back the message property of that object:

return res.status(401).send({ error : err.message });

Also, your second .then() is superfluous, you can shorten your code to this:

userPromise.then(function(user) {
  if (! user) {
    throw new Error("step 1 failed!");
  }
  if (! user.comparePassword(req.body.password)) {
    throw new Error("step 2 failed!");
  }
  return res.json({token: jwt.sign({email:user.email, name:user.name, _id: user._id}, 'SOMETOKEN')});
}).catch(function(err) {
  return res.status(401).send({ error : err.message });
});

Answer 2

在第一个then()块的末尾添加return Promise.resolve(user) 。