Postgres query to return JSON object keys as array

Is it possible to return a JSON object keys as an array of values in PostgreSQL? In JavaScript, this would simply be Object.keys(obj), which returns an array of strings. For example, if I have a table like this: tbl_items --------- id bigserial NOT NULL obj json NOT NULL And if there's a row like this: id obj ----- ------------------------- 123 '{"foo":1,"bar":2}' How can I have a query to return: id keys ----- ------------------ 123 '{"foo","bar"}'