Ajax request on WFS with BBOX doesn't change my number of features

Question

I need to know how many features are displayed on my screen (depending on the BBOX). I read that you can do it with a WFS request and resulttype=hits but my number of features still stay the same, whatever I put in the BBOX. Here's my code :

map.on('moveend', function(evt) {
            var extent = map.getView().calculateExtent(map.getSize());
            console.log(extent);
            var url = 'http://localhost:8080/geoserver/wfs?service=wfs&version=1.1.0&request=getfeature&typename=aisdata:ais_vessels& outputFormat=json&format_options=callback:getJson&resulttype=hits&bbox=' + extent.join(',');
            $.ajax({
                url: url,
                success: function(response) {
                    debugger;
                }
            });
        });

And on the following picture you can see that my BBOX is changing :

Answer 1

It is best to add at the end of the BBOX the SRS of it, as it might not be the same as your data (and WFS defaults to use the SRS of the data if you don't say otherwise). E.g.:

BBOX=-2000000,-2000000,2000000,2000000,EPSG:3857