Using promise all in foreach loop

[Erick Neverson]

Not sure if this is a typical scenario, but I'm trying to populate and array (and eventually an object containing the arrays) recursively with promise all. Below is the code.  What's happening is, after the first iteration, localEncounter never changes again with teh new values.  Where did I go wrong?  Thanks.

var localEncounters = [];
var localEncounter = {};

Promise.all(ids.map(function(id) {

                    return getEncounter(id, client)

                        .then(function (encounter) {

                            encounterObject = encounter;

                            //set the fields for the return object

                            localEncounter['encounterid'] = encounterObject[f_id];

                            localEncounter['screeningid'] = encounterObject[f_screening_id];

                            localEncounter['assessmentid'] = encounterObject[f_clinical_assessment_id];

                            localEncounter['psychevalid'] = encounterObject[f_psych_eval_id];

 

                            //get screening

                            return getScreening(encounterObject[f_screening_id], client);

                        })

                        .then(function (screening) {

                            //set the fields for the return object

                            localEncounter['screeningbegintime'] = screening[f_begin_time];

 

                            //get assessment

                            return getAssessment(localEncounter['assessmentid'], client);

                        })

                        .then(function (assessment) {

                            //set the fields for the return object

                            localEncounter['assessmentbegintime'] = assessment[f_begin_time];

 

                            //get psycheval

                            return getPsychEval(localEncounter['psychevalid'], client);

                        })

                        .then(function (psychEval) {

                            localEncounter['assessmentbegintime'] = psychEval[f_begin_time];

 

                            localEncounters.push(localEncounter);

                        }

                        , function (reason) {

                            console.log(reason); // display reason why the call failed;

                            reject(reason, 'Something went wrong creating the encounter!');

                        })

 

                })).then(function(results) {

                    resolve(localEncounters);

                })

[Wout Mertens]

This code is hard to read.
- avoid "global" state
- a['b'] is easier to read as a.b
- you're using localEncounter across many ids that overwrite the same attributes

Instead, you could e.g. pass your accumulated state with "return promiseFn(…).then(function(res){return {state_and_res});

Wout.

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Wout.
(typed on mobile, excuse terseness)

[Dylan Mikus]

Briefly looked over what you’re doing, and noticed two things.

1. Objects are reference to a place in memory, so when you push localEncounter to localEncounters, you are not pushing a unique clone of localEncounter. If you edit localEncounter in the future, it will edit all instances of it pushed to localEncounters.
2. Why are you creating localEncounter and localEncounters outside of your map function and promises? You could have the map function return a promise for each local encounter and then have Promise.all( ids.map( ... ) ).then(function (localEncounters) { ...}). The result of Promise.all can be local encounters.

Maybe I’m off with what you are doing, but those two things might be related to your issue.

​

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Dylan Mikus
BS in Computer Science from CMU
dbm...@gmail.com