unable to split Firebase functions in multiple files

I'm working with firebase functions and arrived to hundreds of functions, and now it is very hard to manage it in single index.js file as shown in their lots of examples

I tried to split that functions in multiple files like:

--firebase.json
--functions
  --node_modules
  --index.js
  --package.json
  --App
    --groupFunctions.js
    --authFunctions.js
    --storageFunctions.js

In this structure i divide my functions in three categories and put in that three files groupFunctions.js, authFunctions.js, and storageFunctions.js. I then tried to import thise files in index.js, but I don't know why it is not working for me.

Here is groupFunctions.js

var functions = require('firebase-functions');
module.exports = function(){
    exports.onGroupCreate = functions.database.ref('/groups/{groupId}')
        .onWrite(event => {
            console.log(`A group is created in database named:${event.params.groupId}.`);
            // some logic...
            //...
        })
}

Here is index.js file:

var functions = require('firebase-functions');
module.exports = require("./app/groups")();

My editor not giving any warning in this code. But when I deploy this code with firebase deploy --only functions, it does not deploy function. If some functions already exist on firebase console, it remove all functions on deploy.

via Inzamam Malik