Q:

Access firebase fireproof promise local variables in other promise functions in Node.js- avoid global

Below is the working code to access data form firebase. It uses global variable 'Data' array to send it to the final callback function. But I don't want to declare global variable. So is there anyway I can pass my data to every callbacks after it ? below is the code.
var data = {};

getData('myKey', function(){
 console.log("myCompleteData: "+ data); //both Id and finalData 
});

var getData= function(key,callback) {
    return fireproof.child("data").child(key)
    .then(CUSTOM_getData)
    .then(callback)
}

function CUSTOM_getData(snapshot) {

        var id= snapshot.val().id;
        data.id= id;

  return {
    then: function(callback) {

    fireproof.child("otherData").child(data.id)
    .then(CUSTOM_getSomethingFromId)
    .then(callback)
      }

  };
}

function CUSTOM_getSomethingFromId(snapshot) {

            var finalData = snapshot.val().finalData;
            data.finalData = finalData;

      return {
        then: function(callback) {

        callback(data);
          }  
      };
}

And I am new to Node.js. So please let me know if this approach is correct :)

A:

Working code:
var getSomeData = function(key,callback) {

    var data = {};

    fireproof.authWithCustomToken(nconf.get('config:someToken')).then(function(){

        return fireproof.child("data").child(key)

    }).then(function(snapshot){

            data.id= snapshot.val().id;

            return fireproof.child("otherData").child(data.id)

    }).then(function(snapshot){

            data.finalData = snapshot.val().finalData;

            callback(data);

    }, function(error){
            console.log('Error: '+error);
    });
}

