You can use Where and WhereIn to filter results.

Sql

Select count(*) From Table_Name;
Where
    Column1=some_value
and
    Column2=some_another_value;

JsStore

connection.count({
    from: "Table_Name",
    where: {
        Column1: some_value,
        Column2: some_another_value
    }
}).then(function(results) {
    //results will be array of objects.
    console.log(results);
}).catch(function(error) {
    console.log(error);
});

Example