filteredExtent.js

function filteredExtent(markers) {
    var ext = [{
        lat: Infinity,
        lon: Infinity
    }, {
        lat: -Infinity,
        lon: -Infinity
    }];
    var ft = m.features();
    for (var i = 0; i < ft.length; i++) {
        if (!m.filter()(ft[i])) continue;
        var coords = ft[i].geometry.coordinates;
        if (coords[0] < ext[0].lon) ext[0].lon = coords[0];
        if (coords[1] < ext[0].lat) ext[0].lat = coords[1];
        if (coords[0] > ext[1].lon) ext[1].lon = coords[0];
        if (coords[1] > ext[1].lat) ext[1].lat = coords[1];
    }
    return ext;
}