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;