//This code will read the documents from the MongoDB collection 

// (the export functionality) and then writes to a file as JSON. 

// This file is used to read (the import functionality) and 

// insert the JSON into another collection. 

// The code uses MongoDB NodeJS driver.

​

//Reads from the collection inCollection based upon a supplied query, 

//and writes to a file as JSON "out_file.json".

​

const MongoClient = require('mongodb').MongoClient;

const fs = require('fs');

const dbName = 'testDB';

const client = new MongoClient('mongodb://localhost:27017', { useUnifiedTopology:true });

​

client.connect(function(err) {

    //assert.equal(null, err);

    console.log('Connected successfully to server');

    const db = client.db(dbName);

​

    getDocuments(db, function(docs) {

        console.log('Closing connection.');

        client.close();

        // Write to file

        try {

            fs.writeFileSync('out_file.json', JSON.stringify(docs));

            console.log('Done writing to file.');

        }

        catch(err) {

            console.log('Error writing to file', err)

        }

    });

}

​

const getDocuments = function(db, callback) {

    const query = { };  // this is your query criteria

    db.collection("inCollection")

      .find(query)

      .toArray(function(err, result) { 

          if (err) throw err; 

          callback(result); 

    }); 

};