CODEWITHSUNDEEP
javascriptparse-platformpromise
toddg
toddg

Reputation: 2906

Parse JavaScript Promises within Loop not Completing

I just can't seem to get a hang of JavaScript promises.

In Parse, I have an attribute on a user that stores an array of Facebook friends IDs. When a new user logs in through Facebook for the first time I want to iterate through their Facebook friends that are using the app, then update those user's Facebook friends array to include this new user.

So... in user before_save I have this:

var friendsArray = user.get("facebookFriends");
// Iterate through all Facebook friends
_.each(friendsArray, function(facebookId){

   // Retrieve the Facebook friend user 
   var query = new Parse.Query(Parse.User);
   query.equalTo("facebookId", facebookId);

   console.log("this executes");
   query.find().then( function(){
       var user = results[0];
       // This does not execute
       console.log("Need to update " + user.get("displayName") + "'s facebook friends");
       return Parse.Promise.as();
   });
}

My problem is not that different than another previous problem I encountered (Parse JavaScript SDK and Promise Chaining), except that this time I need the results of the async call before I can begin updating the user's Facebook friends array.

Upvotes: 0

Views: 810

Answers (1)

danh
danh

Reputation: 62686

The way to accomplish this is with Parse.Promise.when() which is fulfilled when array of promises passed to it are fulfilled. And the loop can be made prettier as _.map().

var friendsArray = user.get("facebookFriends");
var findQs = _.map(friendsArray, function(facebookId){

    // Retrieve the Facebook friend user 
    var query = new Parse.Query(Parse.User);
    query.equalTo("facebookId", facebookId);

    console.log("this executes");
    return query.find();
});

return Parse.Promise.when(findQs).then(function(){
    var user = results[0];
    // This will work now
    console.log("Need to update " + user.get("displayName") + "'s facebook friends");
    return Parse.Promise.as();
});

The results will be an array of arrays -- since find returns an array --passed as var-args, and underscore _.toArray() is useful here, i.e.

return Parse.Promise.when(finds).then(function() {
    var individualFindResults = _.flatten(_.toArray(arguments));
    // and so on

Upvotes: 1

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