Callback return empty array js

Question

Here is the function with in sql queries call. I need return callback only after all queries done. But it return an empty array How to return array with data after all? `

function getUserSales(days, callback){
  getUserByLastLoginDay(days, function (users) {
    var userArray = [];
    _.each(users, function (user) {
      getMostFavoredCat(user.id, function (cat) {
        if(!cat || cat.length == 0){
         return false;
        } else {
          user.mostFavoredCat = takeMostRepeatingObj(cat);
        }
        getRelatedSaleByCat(user.id, user.mostFavoredCat.id, function (sales) {
          user.sales = sales;
          userArray.push(user)
        })
      })
    })
    callback(userArray);
  })
}

`

parwatcodes · Accepted Answer · 2017-02-22 17:33:35Z

1

callback function first parameter is always an error

callback(null,userArray)

you can make use of async.js for the better control flow

npm i async --save

const async = require('async');

function getUserSales(days, callback){
  getUserByLastLoginDay(days, function (users) {
    var userArray = [];
    async.each(users, function (user, cb) {
      getMostFavoredCat(user.id, function (cat) {
        if(!cat || cat.length == 0){
         return false;
        } else {
          user.mostFavoredCat = takeMostRepeatingObj(cat);
        }
        getRelatedSaleByCat(user.id, user.mostFavoredCat.id, function (sales) {
          user.sales = sales;
          userArray.push(user)
          cb();
        })
      })
    }, (err) => {
        if (err) {
            return callback(err);
        } else {
            callback(null, userArray);
        }
    })
  })
}

edited Feb 22, 2017 at 17:33

answered Feb 22, 2017 at 15:52

parwatcodes

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6 Comments

Edward Gizbreht Over a year ago

Thanks, but i know. And it did not help any way

parwatcodes Over a year ago

does userArray contain the data, please can you put the getUserSales function call

Edward Gizbreht Over a year ago

so i put callback(null, userArray) it still return me empty array.

parwatcodes Over a year ago

first your callback should be callback(null, userArray) it's returning null due to the asynchronous nature of node.js, just do a console.log(userArray) before the callback(), i am sure it will print []

Edward Gizbreht Over a year ago

yes, indeed. the callback return [] before my query will end. I need vice versa, only after query is done, return callback.

|

Rajat · Accepted Answer · 2018-03-08 10:29:13Z

0

I think it will Works:

function getUserSales(days, callback){
 getUserByLastLoginDay(days, function (users) {
   var userArray = [];
   _.each(users, function (user) {
      getMostFavoredCat(user.id, function (cat) {
       if(!cat || cat.length == 0){
       return false;
    } else {
      user.mostFavoredCat = takeMostRepeatingObj(cat);
    }
    getRelatedSaleByCat(user.id, user.mostFavoredCat.id, function (sales) {
      user.sales = sales;
      userArray.push(user)
    })
  })
callback(userArray);
})
})
}

answered Mar 8, 2018 at 10:29

Rajat

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