How to return a value inside a function to another function?

Question

so far I had no more problems and thought I could handle AngularJS a bit.
But now I tried to return a value without any results.
The third line calls my function to fetch a name from the database. But that function doesn't return the result.

$scope.showModal = function ($event,listId) {
    console.log("showModal: "+$event.type+" - id: "+listId);
    console.log("scope.listname: "+getListname(listId));
    $('#edit').modal('toggle');
};

function getListname(listId) {
    var query = 'SELECT name FROM Lists WHERE id=(?)';
    $scope.db.transaction(
        function (transaction) {
            transaction.executeSql(query, [listId],
                function (tx, results) {
                    // console.log("Result: "+results.rows.item(0).name); // works!
                    return results.rows.item(0).name; // returns nothing or not to the sender
                }                      
            );
        }
    );
}

If I use console.log() within executeSql I get a value in the console. But why can't I get my result back to the calling function?

See stackoverflow.com/questions/14220321/…

Felix Kling
– Felix Kling

2014-07-30 14:53:32 +00:00
Commented Jul 30, 2014 at 14:53 — Felix Kling
– Felix Kling, Commented Jul 30, 2014 at 14:53

tymeJV · Accepted Answer · 2014-07-30 14:25:56Z

2

Welcome to the world of async! executeSql is async so use a callback to access the data once that function completes:

function getListname(listId, callback) {
    var query = 'SELECT name FROM Lists WHERE id=(?)';
    $scope.db.transaction(
      function (transaction) {
        transaction.executeSql(query, [listId],
            function (tx, results) {
                // console.log("Result: "+results.rows.item(0).name); // works!
                callback(results.rows.item(0).name); // returns nothing or not to the sender
            }                      
        );
    }
);

And then call it!

getListName(listId, function(name) {
    console.log(name);
});

answered Jul 30, 2014 at 14:25

tymeJV

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Comments

Kaken · Accepted Answer · 2014-07-30 14:51:30Z

1

function getListname(listId) {
     var query = 'SELECT name FROM Lists WHERE id=(?)';
     var deferred = $q.defer();
     transaction.executeSql(query, [listId],
            function (tx, results) {
                 deferred.resolve(results.rows.item(0).name);
            }                      
     );
     return deferred.promise;
  }

Can use like this

 getListname(listId).then(function(name){
     $scope.db.transaction = name;
 });

answered Jul 30, 2014 at 14:51

Kaken

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1 Comment

Timo.Klement Over a year ago

Finally! Thank you ... it works! I just had to change $scope.db.transaction to $scope.listname. My problem was that I tried that deferred but as result I got an object [then, catch, finally] and didn't know what to do with it.

Itay Kinnrot · Accepted Answer · 2014-07-30 14:25:11Z

1

You should use promise in order to write the code in sync way but execute it in async. https://docs.angularjs.org/api/ng/service/$q

answered Jul 30, 2014 at 14:25

Itay Kinnrot

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3 Comments

Timo.Klement Over a year ago

Uh ... I tried to avoid that promise. In the past I had always problems with that because I don't really understand how to use it or how to implement it e.g. to my queries. :-(

Felix Kling Over a year ago

@Tipo: Well, good time to learn more about it :) html5rocks.com/en/tutorials/es6/promises

Timo.Klement Over a year ago

Thank you for that link. I will look after it.

karaxuna · Accepted Answer · 2014-07-30 14:25:45Z

0

Your request is asynchronous, so you should handle it with callback:

function getListname(listId, callback) {
    var query = 'SELECT name FROM Lists WHERE id=(?)';
    $scope.db.transaction(
        function (transaction) {
            transaction.executeSql(query, [listId],
                function (tx, results) {
                // console.log("Result: "+results.rows.item(0).name); // works!
                    callback(results.rows.item(0).name); // returns nothing or not to the sender
                }                      
            );
        }
    );
}

answered Jul 30, 2014 at 14:25

karaxuna

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4 Comments

Timo.Klement Over a year ago

Sorry, but I got an error. I guess the "callback" is an unknown function. The error is: Uncaught TypeError: undefined is not a function

karaxuna Over a year ago

you shall pass callback function as a parameter to getListname like this: getListName(listId, function(name){ you have name variable here });

karaxuna Over a year ago

@Tipo the second function that you pass, will be called when database query operation will be completed

Timo.Klement Over a year ago

Hm, let me try what I think you will tell me here: console.log("scope.listname: "+getListname(listId, function (listname) {$scope.listname = listname;})); Ok this don't show me an error but it also don't show me a result. I guess that I don't understand what you mean. I'm really really sorry. :-(

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