JavaScript static function in callback

Hi I've been trying to clarify this but there's something I'm still confused about. I know that you can't return values from asynchronous functions so I've referenced this answer's top answer Returning value from asynchronous JavaScript method?

What I'm trying to do is use the flickrAPI to get the biggest size image. The flickrAPI allows one to search images, so I use this to get the photo_id, then I use this photo_id to procses another request to the API's getSize method to get the URL for the biggest size photo.

The code looks a little messy as it is, because I have a method called flickrRequest which sends an XMLHttp request and gets back a JSON string. I know that I can achieve what I want by writing the functions as follows:

function flickRQforimage() {
    ...got ID
    function flickrRQforSize() {
        ...got maxsizeURL
        create image based on maxsizeURL here
    }
}

but I was wondering if it was possible to do something like this

function flickRQforimage() {
    ...got ID
    function flickrRQforSize() {
        ...got maxsizeURL

    }
    create image based on maxsizeURL here
}
or even create image based on maxsizeURL here

In general my question is whether it is possible to have a callback function that references another statically defined function (I think?). The specifics of the my function is that it takes a callback and the ID and URL processing happens in those callbacks:

flickrRQ(options, cb) 

I am wondering whether/what would happen if that unnamed function is instead something else, say flickrRQ(options, processPhoto(data)), and then I define the function in a separate method. This just makes sense for me because I want to keep functionality for the URL processing separate in an attempt to make my code cleaner and more readable.

I tried the following below and it didn't work. Nothing prints. I even have a console.log in the processPhoto method. In fact anything inside of the flickrRQforSize method seems to not evaluate

flickrRQforSize(options, function(data) {
    processPhoto(data)
}

even though in the flickrRQforSize definition, a callback function is taken as an argument. I'm suspecting there must be something about functions/async calls that I don't understand.

I hope this is clear -- if not, I can post my actual code.

Here's my code:

var flickrRequest = function(options, xhrRQ, cb) {
    var url, xhr, item, first;
    url = "https://api.flickr.com/services/rest/";
    first = true;

    for (item in options) {
        if (options.hasOwnProperty(item)) {
            url += (first ? "?" : "&") + item + "=" + options[item];    
            //parses to search equest; 
            first = false;
        }
    }
    //XMLHttpRQ to flickr
    if(xhrRQ == 1 ) { 
        xhr = new XMLHttpRequest();
        xhr.onload = function() { cb(this.response); };
        xhr.open('get', url, true);
        xhr.send();
    };
}

var processPhotoSize = function(photoJSON) {
    var parsedJSON = JSON.parse(data); 
    var last = parsedJSON.sizes.size.length;
    console.log(parsedJSON.sizes.size[last-1].source);
    return parsedJSON.sizes.size[last-1].source;
}
...
flickrRequest(options, 1, function(data) {
    ...
    flickrRequest(sizesOptions, 0, function(data) {
            parsedJSON = JSON.parse(data);
            console.log(parsedJSON); 
            processPhotoSize(data); 
        });         
}