Throw not calling catch method

Version: 3.3.4 Node.js: 5.60

throw new Exception(Exception.database);

results in following error: Unhandled rejection (<{“id”:1,“msg”:“Database Exception”}>, no stack trace)

On the contrary reject(new Exception(Exception.database);

causes no issues.

See code -

class Database{
    static cypher(query, params){
        return new Promise(function(fulfill, reject){
            db.cypher({
                query: query,
                params: params
            })
            .then(function(data){
                fulfill(data);
            })
            .catch(function(){
                throw new Exception(Exception.database); // Point A
            })
        });
    }
}

class User{
    // Constructor .etc

    login(){
        var me = this;

        return new Promise(function(fulfill, reject){
            Database.cypher(me.login_query, me.login_params)
            .then(function(data){
                // Returns empty result
                if(!data[0]){
                    throw new Exception(Exception.user_credentials);
                }

                // Assign values
                data = data[0].user.properties;
                me.username = data.username;
                me.firstname = data.firstname;
                me.lastname = data.lastname;
                me.email = data.email;
                fulfill();
            })

            // Database exception
            .catch(function(ex){
                console.log('error caught');  // Point B
            })
        });
    }
}

// construction .etc
x.login_query = 'invalid query here';
x.login(); // should print 'error caught' but instead prints 'unhandled rejection' despite catch

Code at Point B only executes when the throw at Point A is changed from a throw to a call of the reject function.

To my knowledge, bluebird should handle throws exactly the same as it handles calls to the reject function - that is, to pass errors to the promises catch function.

My issue is that bluebird sometimes sends throws to the catch function, but, at other times (like in the example above) it does not. It registers the throw as a rejection but does not call the catch function.

[petkaantonov]

new Promise is not needed when you are dealing with APIs that already return a promise. You can write this equivalent code (for more, see explicit construction anti-pattern):

class Database {
    static cypher(query, params){
        return db.cypher({
            query: query,
            params: params
        }).catch(function() {
            throw new Exception(Exception.database);
        });
    }
}

Your throw statement is indeed inside a different function, that’s why it’s not affecting the upper function:

.catch(function onlyThisFunctionIsAffectedByThrowsAndReturnsInsideThisFunction() {
    throw new Exception(Exception.database);
});

[andyrichardson]

Thank you all for the feedback, apologies for any wasted time.