A function that has nested callback functions does not return values

Question

I have a function inside of which there is a nested callback function structure. I want that first "mother" function to return a certain value, after it's been calculated in the callback functions sequence. However. it doesn't really work. Here's a simplified version of the code, do you think you could help?

console.log(finalResult());

function finalResult() {    

var finalanswer = firstFunction(secondFunction);

function firstFunction (callback) {
    var notion = 1;
    callback(null, notion);
}

function secondFunction (err, notion) {
    if (err) console.log(err);
    var answer = notion + 1
    return answer;
}

return finalanswer;  

}

Thank you!

**UPDATE - THE ORIGINAL CODE**

 return getContexts(makeQuery);


 function getContexts (callback) {

    dbneo.cypherQuery(context_query, function(err, cypherAnswer){

        if(err) {
            err.type = 'neo4j';
            return callback(err);
        }
        // No error? Pass the contexts to makeQuery function
        return callback(null,cypherAnswer);



    });




}

function makeQuery (err,answer) {
    // Error? Display it.
    if (err) console.log(err);

    // Define where we store the new contexts
    var newcontexts = [];

    // This is an array to check if there are any contexts that were not in DB
    var check = [];

    // Go through all the contexts we received from DB and create the newcontexts variable from them
    for (var i=0;i<answer.data.length;i++) {
        newcontexts.push({
            uid: answer.data[i].uid,
            name: answer.data[i].name
        });
        check.push(answer.data[i].name);
    }

    // Now let's check if there are any contexts that were not in the DB, we add them with a unique ID
    contexts.forEach(function(element){
        if (check.indexOf(element) < 0) {
            newcontexts.push({
                uid: uuid.v1(),
                name: element
            });
        }
    });

    return newcontexts;

}

Please post full code .. where are you defining `secondFunction` and how are you calling `finalResult()` — Ramy Nasr, May 27 '14 at 17:45
Sorry, I made a typo when simplifying. actually makeQuery = secondFunction — Aerodynamika, May 27 '14 at 17:53
I just spoke to the spirits of JavaScript developers long gone and they tell me that you're trying to return from an asynchronous function. Are my psychic powers on the mark? — Chuck, May 27 '14 at 17:53
FYI, your code [does work with the return statement suggested by Ramy](http://jsfiddle.net/nY2R9/). — Chuck, May 27 '14 at 17:56
@Chuck - i added the original code... looks like i have another function inside... — Aerodynamika, May 27 '14 at 22:55

Andrew · Answer 1 · 2014-05-28T02:37:38.117

You're setting finalanswer equal to the return of firstFunction however, if you look at the body of firstFunction, it does not return anything. The last line of firstFunction should be:

return callback(null, notion);

I quickly tested this in the Chrome console and it seems to work as expected and logs 2 to the console.

UPDATE

Now that the original code has been posted I would update the code as such:

// call getContexts with a callback when complete
getContexts(function(err, contexts){
    console.log(err);
    console.log(contexts);
});

function getContexts (callback) {
    dbneo.cypherQuery(context_query, function(err, cypherAnswer){
        if(err) {
            err.type = 'neo4j';
            return callback(err);
        }
        // No error? Pass the contexts to makeQuery function
        var contexts = makeQuery(null,cypherAnswer);

        // we have our answer, call the callback
        callback(null, contexts);
    });
}

function makeQuery (err,answer) {
    // Error? Display it.
    if (err) console.log(err);

    // Define where we store the new contexts
    var newcontexts = [];

    // This is an array to check if there are any contexts that were not in DB
    var check = [];

    // Go through all the contexts we received from DB and create the newcontexts variable from them
    for (var i=0;i<answer.data.length;i++) {
        newcontexts.push({
            uid: answer.data[i].uid,
            name: answer.data[i].name
        });
        check.push(answer.data[i].name);
    }

    // Now let's check if there are any contexts that were not in the DB, we add them with a unique ID
    contexts.forEach(function(element){
        if (check.indexOf(element) < 0) {
            newcontexts.push({
                uid: uuid.v1(),
                name: element
            });
        }
    });

    return newcontexts;
}

This will work as long as the code does not make any async calls. The code in the original question does not make async calls so you are correct, but @deemeetree should be aware that this will NOT work as soon as the code makes an async call. — Hector Correa, May 27 '14 at 19:07
The code in the question does not work for you or the code which you're not showing us does not work for you? Based on the code you posted, my answer is correct. If you want help with the code that is not working, I suggest you post that. — Andrew, May 27 '14 at 19:29
@Andrew the original code is above - i added it. looks like my code is not working because the return of the second function is nested inside a database query function and probably its return is not the return of the function... but i don't know how to solve it... — Aerodynamika, May 27 '14 at 22:55
Check my updated answer. As others already pointed out, you called a function asynchronously and tried to return a value from within that function. the better approach here is to pass an anonymous function into getContexts that will get called when the asynchronous function is finished. Then you can log your answer as shown. — Andrew, May 28 '14 at 02:40

A function that has nested callback functions does not return values

1 Answers1