How to get host in app.js for use in determining environment (production/development)

Question

I'm trying to get the host the app is currently on and then change a variable accordingly. I know I can use req.get('host') to get the host but I believe my problem stems from callbacks

var callBackUrl;

app.use(function(req,res,next){
    if(req.get('host') == 'localhost:3000'){
        callBackUrl = 'http://localhost:3000/handleauth'; 
    }
    else{
        callBackUrl = 'http://example.com/handleauth';
    }
    console.log('CALL BACK URL: ', callBackUrl); 
    next();
});

console.log(callBackUrl); //undefined

app.use('/', routes);
... //more code

I would like to make a note that I have read about asynchronicity and understand why console.log prints undefined . I simply do not know how to tie callbacks in with req and res .

req.host returns a value correctly. I simply need to get the current host and then use it for authentication purposes (production vs. development)

EDIT: Perhaps this additional code will help others in understanding what I am trying to accomplish

//... original code from question

passport.use(new InstagramStrategy({
    clientID: INSTAGRAM_CLIENT_ID,
    clientSecret: INSTAGRAM_CLIENT_SECRET,
    callbackURL: callBackUrl //set to undefined and therefore authentication fails 
},
function(accessToken, refreshToken, profile, done){
    process.nextTick(function(){
        app.set('instaID', profile.id.toString());
        app.set('fullName', profile.displayName);
        app.set('imgSource', profile._json.data.profile_picture);

        return done(null,profile.id);
    });
}));

Answer 1

I think you should use if else like this;

var callBackUrl;

app.use(function(req,res,next){
    if(req.get('host') == 'localhost:3000'){
         callBackUrl = 'http://localhost:3000/handleauth';
         console.log('CALL BACK URL: ', callBackUrl); 
         next(); 
    }
    else{
         callBackUrl = 'http://example.com/handleauth';
         console.log('CALL BACK URL: ', callBackUrl); 
         next();
     }
 });

console.log(callBackUrl); //undefined

app.use('/', routes);
... //more code

Answer 2

I was able to fix this problem by moving all the authentication code into the app.use callback. If anyone has another solution please let me know. It just seems strange to me to stick that entire block of code in there just to access the value of one variable.

var callBackUrl;

app.use(function(req,res, next){
    if(req.get('host') == 'localhost:3000'){
        callBackUrl = 'http://localhost:3000/handleauth'; 
    }
    else{
        callBackUrl = 'http://example.com/handleauth';
    }
    console.log('CALL BACK URL: ', callBackUrl);

    passport.serializeUser(function(user,done){
        done(null,user);
    });

    passport.deserializeUser(function(obj,done){
        done(null,obj);
    });

    passport.use(new InstagramStrategy({
        clientID: INSTAGRAM_CLIENT_ID,
        clientSecret: INSTAGRAM_CLIENT_SECRET,
        callbackURL: callBackUrl //no longer undefined
    },
    function(accessToken, refreshToken, profile, done){
        process.nextTick(function(){
            app.set('instaID', profile.id.toString());
            app.set('fullName', profile.displayName);
            app.set('imgSource', profile._json.data.profile_picture);

            return done(null,profile.id);
        });
    }));

    next();
});

console.log("URL: ", callBackUrl) //still prints undefined but that it ok since we use the value of callBackUrl inside the callback

app.use('/', routes);