Export a MongoDB collection and write to a CSV. Uses json2csv, async/await, and dotenv.

mongo-export-csv.js

require('dotenv').config();
const { AsyncParser } = require('json2csv');
const fs = require('fs');
const MongoClient = require('mongodb').MongoClient;

const url = `mongodb://localhost:27017`;

const HEADERS = ['first_name', 'last_name', 'middle_name', 'id'];
const FIELDS = ['name.first_name', 'name.last_name', 'name.middle_name', 'id'];

(async function() {
	const client = new MongoClient(url);

	try {
		await client.connect();
		console.log(`successfully connected to server at ${url}`);

		const db = client.db(process.env.DB); // database you want to connect to.
		const coll = db.collection(process.env.COLLECTION); // collection you want to export.
		const documents = await coll.find({}).toArray(); // return all documents in the collection.
		console.log(`found ${documents.length} documents`);

		await writeCsv(documents);
	} catch (err) {
		console.log('oh no! error occurred ', err.stack);
	}

	client.close();
})();

/**
 * Build an array of objects that maps a column's title
 * to it's value within a MongoDB Document.
 * We can map the headers to the values because there should always be the same
 * number of each, and they should be in the same order.
 *
 * Resulting array will look something like this
 * [
 * 	{
 * 		label: 'FirstName', // how it appears in the CSV
 * 		value: 'name.first_name', // where the value is found.
 * 		default: null, // what to input if the value is not found within the document.
 * 	},
 * 	{...}
 * ]
 */
const makeFields = () => {
	let fields = [];
	HEADERS.map((header, i) => {
		fields.push({
			label: header,
			value: FIELDS[i],
			default: null,
		});
	});

	return fields;
};

const writeCsv = async records => {
	const dir = __dirname + '/csv/';
	const filename = `output_${Date.now()}.csv`;
	const path = `${dir}${filename}`;

	// Check that /path/to/csv/ directory exists and create it if it does not.
	if (!fs.existsSync(dir)) {
		fs.mkdirSync(dir);
	}
	fs.createWriteStream(path);

	let csv = '';
	let fields = makeFields();
	const parser = new AsyncParser({
		fields,
		unwind: ['name'],
	});

	// Parse the data into a string.
	parser.processor
		.on('data', chunk => {
			csv += chunk.toString();
		})
		.on('end', () => {
			console.log('data has been parsed successfully!');
			// write the resulting string (`csv`) to a file.
			fs.writeFile(path, csv, err => {
				if (err) {
					return console.error('Error occurred while creating csv ', err);
				}
				console.log(`csv file written successfully at ${path}`);
				return csv;
			});
		})
		.on('error', err =>
			console.error('oh no! an error occurred while parsing data: ', err)
		);

	parser.input.push(JSON.stringify(records)); // feed the data into our parser.
	parser.input.push(null); // Sending `null` to a stream signal that no more data is expected and ends it.
};