Javascript array length of 0

I am getting some weird behaviour with the following, it shows an array length of 0 eventhough printing it right before that shows that there clearly is a length greater than 0:

var getTopSelection = function(callback) {
    var topSelection = [];
    for(var i=0; i < markers.length; i++) {
        if(markers[i].map !== null) {
            var stationID = markers[i].id;
            getTrips(stationID, globalFromDate, globalToDate, function(response) {
                topSelection.push({
                    StationID: stationID,
                    Trips: response
                });
            }, function(error) {
                console.log(error);
            })
        }
    }
    callback(topSelection);
};

getTopSelection(function(response) {
            console.log(response); //115
            console.log(response.length); //116
})

And this is shown in the inspector, the "length: 42" belongs to line 115.

Question: Why does it show a length of 0 eventhough it clearly says it has a length of 42 one line before?