Accessing 'this' inside a callback?

Question

This question relates to my previous question but I am now experiencing a different error.

I have a series of promises, before each execution, I check whether the user has cancelled the promise chain.

My issue is, I cannot access 'this' inside the call back methods, a crude example is below, I cannot access the p.test variable inside getMoreData()

p.test = 'hello!';

p.init = function(){

    this.getData() 
    .then(function(data) {
        return shouldContinue(getMoreData,data);
    })
}

p.shouldContinue = function(cb, data){
   ...
  this.currentRequest = cb.call(this,data);
};

p.getData = function(){
    //return ajax call
};

p.getMoreData = function(){
    console.log(this.test); //undefined
    //return ajax call
};