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

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.

via Kunal