NodeJS: How to convert 'aggregation'(cursor) object to CSV and return a CSV response from a request using Express?

I want to convert the result from aggregate to a csv. In the code (or pseudocode) below the results of the aggregate are stored in variable cursor

I want to return a csv as a response ( res.send(csv) ). Do I have to use res.set('Content-Type', 'content-type: text/csv') ?

The code below is a mix of NodeJs and pseudocode. Function covert_to_csv indicates my ignorance about the subject.

const express = require('express')
const app = express();

app.get('/', (req, res) => {
    let agg=[ /*   a query in MongoDB   */]

    MongoClient.connect(URL,(err, client) => {

        res.set('Content-Type', 'content-type: text/csv');

        let collection = client.db('db').collection('col')
        let cursor = collection.aggregate(agg)

        let csv_file = covert_to_csv(cursor)

        csv_file.toArray((error, result) => {
            res.send(result);
    });

});

app.listen(port, () => console.log(`listening on port ${port}!`));

Edit:

I am getting this response from Postman in JSON :

[
    {
        "Source": "entso-e",
        "Dataset": "ActualTotalLoad",
        "AreaName": "Germany",
        "AreaTypeCode": "CTY",
        "MapCode": "DE",
        "ResolutionCode": "PT15M",
        "Year": "2018",
        "Month": "1",
        "Day": "2",
        "DateTimeUTC": "2018-01-02 00:00:00.0000000",
        "ActualTotalLoadValue": "41412.38",
        "UpdateTimeUTC": "2018-01-02 13:16:19.0000000"
    },
    {
        "Source": "entso-e",
        "Dataset": "ActualTotalLoad",
        "AreaName": "Germany",
        "AreaTypeCode": "CTY",
        "MapCode": "DE",
        "ResolutionCode": "PT15M",
        "Year": "2018",
        "Month": "1",
        "Day": "2",
        "DateTimeUTC": "2018-01-02 00:45:00.0000000",
        "ActualTotalLoadValue": "40785.17",
        "UpdateTimeUTC": "2018-01-02 13:16:19.0000000"
    },
    ..... (more documents)
    ]

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