This function returns a JSON with the array's item ocurrence counting. It only works on Postgres >= 9.4

count_array_items.sql

create function count_elements(text[]) returns json as $body$
  select
    json_object_agg(key, value)
  from (
    select
      item as key,
      count(*) as value
    from (select unnest($1) item) as item
    group by item
  ) agg;
  $body$
language sql;

select count_elements(array['foo', 'foo', 'bar']);
-- { "foo" : 2, "bar" : 1 }