nodeJs returning QUOTED string instead of plain text using lambda AWS

The nodejs function is expected to return text/csv but instead returning quoted string with embedded newline character \n instead of real newline.

Using interceptor for headers received in response it states correctly content-type: text/csv for request like GET /tst/items/name HTTP/1.1 The nodejs snippet is

 const Json2csvP = require('json2csv').Parser;
 const fields = ['f1','f2','f3'];
var searchQ =['select * from names'];
 await db.any(searchQ[0])
        .then(function(data) {
           const json2csvP = new Json2csvP({ fields, quote: '', eol: '\n' });
            console.log(csv);
            callback(null, (csv));
        })

so for the console response in AWS output is like

"field1, field2 field3\n1  2  3"

and the caller in browser/REST tool get it

"field1, field2 field3\n1  2  3"

but I am looking the below csv format at callee side

field1 field2 field3
1  2   3

note there is no quote, and a real new line instead of \n character in plain text without html.I did tried using .split like below

 callback(null, (csv).split(/\n/g));

that give real newline only in AWS response result ["field1 field2 field3", "1 2 3"]

but not in the format desired (without quotes in both line) and for the caller/ browser/REST tool , it gave like below without newline and with quotes and extra undesired [ and ] characters like like below.

["field1 field2 field3", "1  2   3"]

How can caller receive the below?

field1 field2 field3
    1  2   3