passpostJS-FacebookStrategy-Callback.js

// Configure the Facebook strategy for use by Passport.
passport.use(new Strategy({ //This is class constructor argument telling Passport to create a new Facebook Auth Strategy
    clientID: process.env['FACEBOOK_CLIENT_ID'],//The App ID generated when app was created on https://developers.facebook.com/
    clientSecret: process.env['FACEBOOK_CLIENT_SECRET'],//The App Secret generated when app was created on https://developers.facebook.com/
    callbackURL: 'http://localhost:3000/api/v1/user/return',
    profile: ['id', 'displayName'] // You have the option to specify the profile objects you want returned
  },
  function(accessToken, refreshToken, profile, done) {
    //Check the DB to find a User with the profile.id
    User.findOne({ facebook_id: profile.id }, function(err, user) {//See if a User already exists with the Facebook ID
      if(err) {
        console.log(err);  // handle errors!
      }
      
      if (user) {
        done(null, user); //If User already exists login as stated on line 10 return User
      } else { //else create a new User
        user = new User({
          facebook_id: profile.id, //pass in the id and displayName params from Facebook
          name: profile.displayName
        });
        user.save(function(err) { //Save User if there are no errors else redirect to login route
          if(err) {
            console.log(err);  // handle errors!
          } else {
            console.log("saving user ...");
            done(null, user);
          }
        });
      }
    });
  }
));