From my understanding of jQuery, .then() is an asynchronous call. This means that, the .then() function will be called after the coords_obj query returns a result, but any code outside will be carried out without waiting for query result.

The following line:

alert(lat);

, is outside the .then() function. Therefore, it gets called before the query returns a result. But the wierd part is that it doesn't even show the default value 0 . I noticed that console.log(lat) works in such cases, instead of using alert(lat).

Try modifying the code like this:

if (coords){

                var coords_obj = new openerp.Model('gps_base.coords');
                coords_obj.query(['latitude_aux', 'longitude_aux'])
                     .filter([['id', '=', coords]])
                     .limit(1)
                     .all().then(function (result) {
                            _.each(result, function(item) {
                                lat=item.latitude_aux;
                                lng=item.longitude_aux;

self.latLngFunction(lat,lng); //This way, lat and lng are displayed correctly

                            });
                        });
            },

// After the above function body, create a new function similar to the one below:

latLngFunction:function(lat,lng)
        {
            console.log("Latitude",lat); // You can view this result in your browser console
            console.log("Longitute",lng);
            // OR
            alert(lat); //Now the alert should display a proper value.
            alert(lng);
        },

Many thanks Swahn but no, it didn't work. You did set me in the proper direction and, after looking for widget code in the Odoo modules, I eventually came to write this:

          function get_coordinates(coords_id){

                var result = new $.Deferred();
                new instance.web.Model('gps_base.coords')
                    .query(['latitude_aux', 'longitude_aux'])
                    .filter([["id", "=", coords_id]])
                    .first()
                    .then(function(records){
                        if(!records || records.length === 0){
                            result.reject();
                        }else{
                            result.resolve(records);
                        }
                    });
                return result;
            }
 

            if (coords){
                query_res=get_coordinates(coords);
                alert(query_res.latitude_aux);
            }

But, unfortunately, I never get a proper value. I'm lost. It seems no matter what example I follow, it never works. Has to be something really silly I am missing here... :(