NodeJS: recursive function with async request

Question

I'm trying to transfer 2 results from 2 callback to 1 lodash function (_.union) using recursive function. I dont understand what am I doing wrong! I keep getting "undefined". Here is my code:

EDITED:

My new code with the "promise" technique

the first function that check things in the remote DB-

function findFiles(kw, callback){
    if (_.isArray(kw)) {return callback(kw)};

    return new Promise((resolve, reject) => {
        console.log(kw);
        word.aggregate([
                     { $match: { keyWord: kw } },
                     { $project: { filesFound: '$filesFound.fileName' , '_id':0} },
                     { $sort: { fileName: 1 } }
                   ],function(err, obj){
                    console.log('checked' + kw);
                    console.log(obj);
            if (err) return reject(err);
            else      
                return resolve(obj[0].filesFound);//obj[0].filesFound
        })
    })
}

The main function:

    function searchOperation(query, callback){
    var stack=[];
    if (!(_.includes(query, 'OR')) && !(_.includes(query, 'AND')) && !(_.includes(query, 'NOT'))){

        findFiles(query)
        .then((item) => {
            console.log(item+'********');   
           callback(item)
        })
        .catch((err) => {
          console.log(err)
        })
    }
    else{
        wordsArr = _.split(query, " ");
        console.log("+++++:" + wordsArr);
        wordsArr.forEach(function(w){
            console.log('first check:'+w);

            if(_.isEmpty(stack)){

                if(_.includes(w, 'OR')){
                    console.log('found OR');
                    var statement = [];
                    console.log('query is:'+query);
                    statement = _.split(query, w, 2);
                    console.log(statement[0]+' , '+statement[1]);
                    return new Promise((resolve, reject)=>{


    resolve(_.union(searchOperation(statement[0]),searchOperation(statement[1])))
                        })
//ANOTHER OPTION:
                        // searchOperation(statement[0],function(arr1){
                        //     console.log('arr1');
                        //     console.log('done part 1!');
                        //     searchOperation(statement[1],function(arr2){
                        //         console.log('who called arr2?');
                        //         return(_.union(arr1,arr2));
                        //     })
                        // });
                    }
                }
            })
        }
    }

now, inside the function findFile() the console.log return what i need. but then I need to use both returned values in another function (union) and it returns undefined.

in the main thread:

searchOperation('Expression1 OR Expression2', function(result){
    res.json(result);
})

now i'm sure: something goes WRONG in the recursive function and the async of node...

I need it to work recursively and could get complicate expressions like:

'((A NOT B) AND (C OR D))'

does some know what is the right way to write it either with Promise or async.waterfall ?? thanks in advance!!!

Possible duplicate of How do I return the response from an asynchronous call? — gyre
– gyre, Commented Mar 5, 2017 at 8:43

Nijikokun · Accepted Answer · 2017-03-05 08:52:53Z

1

Your code doesn't work because you're trying to get an Async response in a Synchronous fashion.

Look into Promises.

answered Mar 5, 2017 at 8:52

Nijikokun

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3 Comments

DavidA Over a year ago

do you know what is the right way to write it with async.waterfall?

Nijikokun Over a year ago

You would pass a callback or use a promise in your query function and invoke the callback upon completion of the waterfall callbacks basically resolve your promise in the waterfall invocation: npmjs.com/package/async-waterfall#tasks-as-array-of-functions

DavidA Over a year ago

thank you, I saw it already. still don't know how to combine it with my code... :(

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