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Hi, how I can make sql query from javascript? I'm new.

I'm not sure exactly what you are asking but have you checked the supabase docs and followed any of the examples? You should try that first if you are new and get more familiar with the library.

create or replace function get_messages() 
returns setof messages as $$

    var json_result = plv8.execute(
        'select * from messages'
    );

    return json_result;

an example in javascript of the plv8: Javascript Language