Can't get return value from javascript function

Question

I don't know what the problem is. It keeps returning an empty array. That is, movieIds is always empty.

function getMoviesInCinema(theCinema){
    var cinema = theCinema;
    var query = new Parse.Query("showing");
    var movieIds = [];

    query.equalTo("cinema", {
        __type: "Pointer",
        className: "Cinema",
        objectId: cinema
    });
    query.find().then(function(results) {
        if(results.length > 0){
            for (var i = 0; i < results.length; i++) {
                movieIds.push(results[i].get("movie"));
            }

        }
        else{
            console.log("Could be an error");
        }
    });
    return movieIds;

}

score 2 · Answer 1 · answered Aug 30 '14 at 09:13

That's because the query hasn't finished yet when you return from the function. You should make your function take a callback instead:

function getMoviesInCinema(theCinema, callback){
    var cinema = theCinema;
    var query = new Parse.Query("showing");

    query.equalTo("cinema", {
        __type: "Pointer",
        className: "Cinema",
        objectId: cinema
    });
    query.find().then(function(results) {
        if(results.length > 0){
            callback(results);
        }
        else{
            console.log("Could be an error");
        }
    });
}

Then call it as such:

getMoviesInCinema(theCinema, function(movieIds) {

    console.log(movieIds);

});

I need the result of the query as a varable as such. var VariableName = resultofquery — user3679294, Aug 30 '14 at 09:21
@user3679294: You can't, at least not in a way that lets you usefully use the array immediately. Again, as James said, your function returns **before** the information is available. — T.J. Crowder, Aug 30 '14 at 09:22

score 0 · Answer 2 · answered Aug 30 '14 at 09:14

The issue here is that query.find() runs asynchronously. That means your getMoviesInCinema function returns before query.find calls your then callback.

Because query.find is asynchronous, your function cannot return the IDs directly. (It can return the array, but the array will be empty to start with.) Instead, it should also provide a Promise or allow for a callback.

Not sure what Promises lib you're using, so here's the option using a callback:

function getMoviesInCinema(theCinema, callback){
// Receive the callback --------------^
    var cinema = theCinema;
    var query = new Parse.Query("showing");
    var movieIds = [];

    query.equalTo("cinema", {
        __type: "Pointer",
        className: "Cinema",
        objectId: cinema
    });
    query.find().then(function(results) {
        if(results.length > 0){
            for (var i = 0; i < results.length; i++) {
                movieIds.push(results[i].get("movie"));
            }

        }
        else{
            console.log("Could be an error");
        }
        if (callback) {             // <=====
            callback(movieIds);     // <===== Call it
        }                           // <=====
    });
}

Usage:

getMoviesInCinema(42, function(movieIds) {
    // Use movieIds here
});

score -3 · Answer 3 · answered Aug 30 '14 at 09:12

-3

Instead of using

movieIds.push(results[i].get("movie"));

Try using

movieIds.add(results[i].get("movie"));

It might solve your problem.

answered Aug 30 '14 at 09:12

Prashant2329

327
3
7
21

can u try printing "results[i].get("movie")" ... – Prashant2329 Aug 30 '14 at 09:17
1

This is even more incorrect that the OP's original code and is unrelated to the actual issue. `.push` is the correct method for adding something to the end of an array (`[].add` does not exist). – Qantas 94 Heavy Aug 30 '14 at 09:18
and 1 more thing declare var movieIds in global scope .. – Prashant2329 Aug 30 '14 at 09:18
*"and 1 more thing declare var movieIds in global scope"* That's even worse advice than the answer. – T.J. Crowder Aug 30 '14 at 09:22

Can't get return value from javascript function

3 Answers3