Get value out of function in Node.js

Question

I don't know about the correct title for my problem. I just need a value going out of a function, just like return but I think it's not same. i have code snippet from controller in adonisjs framework:

var nmeadata = "";
jsondata.forEach(element => {
    var x = element.nmea
    var buff = new Buffer(x, 'base64')
    zlib.unzip(buff, (err, res) => {
        if(err)
        {
            //
        }
        else
        {
            nmeadata += "greed island"
            nmeadata += res.toString()
        }
    })
});

return view.render('admin.index', {
    data: datanmea.toJSON(),
    nmea: nmeadata
})

I need the result of unzipped string data that inserted to nmeadata from zlib function then send it to view. But, for this time, even I cannot displaying a simple output like greed island to my view.

thank you.

UPDATE

Still not working after using promises:

class NmeaController {

    async index({view})
    {
        
        const datanmea = await NmeaModel.all()
        const jsondata = datanmea.toJSON()

        var promises = [];
        var nmeadata = "";
        jsondata.forEach(element => {
            promises.push(
                new Promise(resolve => {
                    let x = element.nmea
                    let buff = new Buffer(x, 'base64')
                    zlib.unzip(buff,
                        (err, res) => {
                            if (err) {
                            //
                            } else {
                            nmeadata += "test add text"
                            // nmeadata += res.toString()
                            }
                            //im also try using resolve() and resolve("any text")
                            resolve(nmeadata);
                        })
                    }
                )
            )
        });
        await Promise.all(promises);
        return view.render('admin.index', {
            data: datanmea.toJSON(),
            nmea: nmeadata
        });
    }

UPDATE AUGUST 22 2019

i'm already tried solution from maksbd19 but still not working

class NmeaController {

    async index({view})
    {
        
        const datanmea = await NmeaModel.all()
        const jsondata = datanmea.toJSON()

        var promises = [];
        var nmeadata = "";
        jsondata.forEach(element => {
            promises.push(
                new Promise(resolve => {
                    let x = element.nmea
                    let buff = new Buffer(x, 'base64')
                    zlib.unzip(buff,
                        (err, res) => {
                            if (err) {
                                // since you are interested in the text only, so no need to reject here
                                return resolve("");
                            }
                            return resolve("greed island")
                        })
                    }
                )
            )
        });
        const result = await Promise.all(promises); // this will be an array of results of each promises respectively.
        nmeadata = result.join(""); // process the array of result 
        return view.render('admin.index', {
            data: datanmea.toJSON(),
            nmea: nmeadata
        });
    }
}

Possible duplicate of [How do I return the response from an asynchronous call?](https://stackoverflow.com/questions/14220321/how-do-i-return-the-response-from-an-asynchronous-call) — CertainPerformance, Aug 05 '19 at 08:10
Convert the callback API to promises, then call `Promise.all` on an array of promises — CertainPerformance, Aug 05 '19 at 08:11
async function foo() { var url= 'https://jsonplaceholder.typicode.com/todos/1'; var result= await (await fetch(url)).text(); // or .json() return result; } async function load() { var result = await foo(); console.log(result); } load(); — putra irawan, Aug 19 '19 at 12:39
Try to add await when converting datanmea to JSON: const jsondata = await datanmea.toJSON() — asubanovsky, Aug 20 '19 at 15:34

score 0 · Answer 1 · answered Aug 20 '19 at 07:18

I'd suggest two things-

modify zlib.unzip callback function to resolve properly;

(err, res) => {
    if (err) {
        // since you are interested in the text only, so no need to reject here
        return resolve("");
    }
    return resolve(res.toString())
}

retrieve the final data from the result of Promise.all

const result = await Promise.all(promises); // this will be an array of results of each promises respectively.
nmeadata = result.join(""); // process the array of result

In this approach every promise will resolve and finally you will get the expected result in array.

Get value out of function in Node.js

UPDATE

UPDATE AUGUST 22 2019

1 Answers1