const filterByName = null;
const filterPopLow = 1000;
const filterPopHigh = 10000;

let query = supabase
  .from("cities")
  .select("name, country_id");

if (filterByName)  { query = query.eq("name", filterByName) }
if (filterPopLow)  { query = query.gte("population", filterPopLow) }
if (filterPopHigh) { query = query.lt("population", filterPopHigh) }

const { data, error } = await query;