CODEWITHSUNDEEP
javascriptangularjs
Manuel RODRIGUEZ
Manuel RODRIGUEZ

Reputation: 2161

Is forEach() asynchronous?

I am trying to rank a list of user based on how many times they appear in several list:

function getRegistrationsFromSportList(sportList){
        console.info('[DatabaseService-getRegistrationsFromSportList] Getting registrations to sports...');
        var promiseHash = {};
        sportList.forEach(function (sport){
          promiseHash[sport] = firebase.database().ref('/sport_registrations/' + sport).once('value');
        });
        return $q.all(promiseHash);
      }

      getUserSportListPromise(user.uid).then(function(sportList){
        return getRegistrationsFromSportList(sportList);
      })
      .then(function(registrationsHash){
        console.info('[DatabaseService-getMatches] Processing matches...');
        var matches = [];
        angular.forEach(registrationsHash, function(regsSnap, sport){
          console.dir(regsSnap.val());
          regsSnap.forEach(function(user){
              if (matches.indexOf(user.key) > -1) {
                matches[user.key]++;
              } else{
                matches[user.key] = 1;
              }
              console.dir(matches);
          });
        });
      });
    }

Here is my console log:

Object
 e8wXuTklnVcYknc0MYn34xlcqmA3: true

Array[0]
 Lvwr4lkZ58SnhrZzft6FhT08iVN2: 1
 ND9iZYJ3gfQUvjKSRaKKc8NEkAj2: 1
 SA0h1iHwyCSeytgh6FOglSf1sOs2: 1
 e8wXuTklnVcYknc0MYn34xlcqmA3: 1

Object
 Lvwr4lkZ58SnhrZzft6FhT08iVN2: true
 ND9iZYJ3gfQUvjKSRaKKc8NEkAj2: true
 SA0h1iHwyCSeytgh6FOglSf1sOs2: true
 e8wXuTklnVcYknc0MYn34xlcqmA3: true

Array[0]
 Lvwr4lkZ58SnhrZzft6FhT08iVN2: 1
 ND9iZYJ3gfQUvjKSRaKKc8NEkAj2: 1
 SA0h1iHwyCSeytgh6FOglSf1sOs2: 1
 e8wXuTklnVcYknc0MYn34xlcqmA3: 1
  1. Why is my first console.info() displaying the matches array filled with the results of the second Object of regsSnap? I don't understand why this is happening while I am calling console.info() within the forEach() function
  2. I guess strongly related to point 1 but I was expecting e8wXuTklnVcYknc0MYn34xlcqmA3 to be equal to 2
  3. Why the console displays Array[0] instead of Array[3]?

Any suggestion? Help?

Thanks!

Upvotes: 2

Views: 2888

Answers (1)

Dvid Silva
Dvid Silva

Reputation: 1162

No, forEach() is not async, both the angular or native one.

For the first question, I don't think there's enough code to see why your code behaves that way, what is returned by the others? can you paste the full console output?.

For your second question, this comparison is always false, matches.indexOf(user.key) > -1, is better if you use if (matches[user.key] ) or even a tertiary expression like:

matches[user.key] = matches[user.key] ? matches[user.key] + 1 : 0;

For the third question, because you haven't pushed any element to the array, you're adding values to keys, but technically the array has zero elements until you use numeric keys or use the push method. Either change matches to be an object, or change the way you store and retrieve information from it.

Upvotes: 5

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