Iterate over an array using async js and executing a function inside callback to return a single result

Question

I'm running a Node Js server and I'm receiving the following content from my frontend:

{
  dataType: "any",
  fechaI: "any",
  fechaF: "any",
  checkedList: [ "any obj","any obj"]
}

I have to iterate over the checkedList array in order to get the action property of all of its objects and then make use of the import for queries

const query = require("./queries.js")

query[item.action](req,res,resp,function(err,data){
            console.log(data)
        })

I want to set a variable with all the results of the query after the iteration is complete, I have tried using async.each but the queries return undefined objects. Also all the other properties of the content I get aren't passed to the query item properly.

Here's what I have tried so far:

    async.each(checkedList ,function(item, next) {
       let results =[]
 
        query[item.action](req, res, resp, function(err, data) {
            console.log(data)
            results.push(data)
            console.log(results)
            next()
        }.bind({results:results}))
    }, function(err) {
        if (err) console.log(err)
        console.log('done')
    })

The output of console.log(data) is undefined however results does return a value but it belongs to the last item of the array. What am I doing wrong in this scenario?

Might as well use a regular loop since you want a result after all of those async executions. Otherwise, create a bunch of Promises and use Promise.all(). — StackSlave
– StackSlave, Commented Feb 6, 2020 at 1:47
so i would have to make the query a promise and then i should map the results to the array? — VicSan
– VicSan, Commented Feb 6, 2020 at 1:56
Oh, I see you want to do querys. Keeping the async loop makes sense. Wrap the query in a Promise that is resolved after your results.push(data). Then pass all those Promises into Promise.all(). — StackSlave
– StackSlave, Commented Feb 6, 2020 at 2:12
Could you answer how would that look? It would be very helpful — VicSan
– VicSan, Commented Feb 6, 2020 at 2:31

StackSlave · Accepted Answer · 2020-02-06 03:30:24Z

1

After reviewing your code I think, but am not sure, you want to do something like:

function whatever(){
  const listData = [];
  return new Promise((resolve, reject)=>{
    async.each(checkedList, (item, next)=>{
      query[item.action](req, res, resp, (err, data)=>{
        listData.push(data);
        if(listData.length === checkedList.length)resolve(listData);
        next();
      });
    }, err=>{
      console.log(err); reject(err);
    });
  });
}
whatever().then(listRes=>{
  console.log(listRes);
});

Personally, I would just call a function when you have all your results instead of returning something:

function whatever(doneFunc){
  const listData = [];
  async.each(checkedList, (item, next)=>{
    query[item.action](req, res, resp, (err, data)=>{
      listData.push(data);
      if(listData.length === checkedList.length)doneFunc(listData);
      next();
    });
  }, err=>{
     console.log(err);
  });
}
whatever(listRes=>{
  console.log(listRes);
});

answered Feb 6, 2020 at 3:30

StackSlave

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1 Comment

VicSan Over a year ago

when i have an array of two or more items the function returns an error saying ` Error: Callback was already called.`

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