Building a Bulk Asynchronous Bird Recipient Validation Tool

let count = 0; // Line count
require("fs")
    .createReadStream(myArgs[1])
    .on("data", function (chunk) {
        for (let i = 0; i < chunk.length; ++i)
            if (chunk[i] == 10) count++;
    })
    // Reads the infile and increases the count for each line
    .on("close", function () {
        // At the end of the infile, after all lines have been counted, run the recipient validation function
        validateRecipients.validateRecipients(count, myArgs);
    });

async function validateRecipients(email_count, myArgs) {
    if (
        // If both the infile and outfile are in .csv format
        extname(myArgs[1]).toLowerCase() == ".csv" &&
        extname(myArgs[3]).toLowerCase() == ".csv"
    ) {
        let completed = 0; // Counter for each API call
        email_count++; // Line counter returns #lines - 1, this corrects the number of lines
        // Start a timer
        const { window } = new JSDOM();
        const start = window.performance.now();
        const output = fs.createWriteStream(myArgs[3]); // Outfile
        output.write(
            "Email,Valid,Result,Reason,Is_Role,Is_Disposable,Is_Free,Delivery_Confidence\n"
        ); // Write the headers in the outfile
    }
}

fs.createReadStream(myArgs[1])
    .pipe(csv.parse({ headers: false }))
    .on("data", async (email) => {
        let url =
            SPARKPOST_HOST +
            "/api/v1/recipient-validation/single/" +
            email;
        await axios
            .get(url, {
                headers: {
                    Authorization: SPARKPOST_API_KEY,
                },
            });
        // For each row read in from the infile, call the SparkPost Recipient Validation API
    });

.then(function (response) {
    response.data.results.email = String(email); 
    // Adds the email as a value/key pair to the response JSON for output
    response.data.results.reason ? null : (response.data.results.reason = ""); 
    // If reason is null, set it to blank so the CSV is uniform
    // Utilizes json-2-csv to convert the JSON to CSV format and output
    let options = {
        prependHeader: false, // Disables JSON values from being added as header rows for every line
        keys: [
            "results.email",
            "results.valid",
            "results.result",
            "results.reason",
            "results.is_role",
            "results.is_disposable",
            "results.is_free",
            "results.delivery_confidence",
        ], // Sets the order of keys
    };
    let json2csvCallback = function (err, csv) {
        if (err) throw err;
        output.write(`${csv}\n`);
    };
    converter.json2csv(response.data, json2csvCallback, options);
    completed++; // Increase the API counter
    process.stdout.write(`Done with ${completed} / ${email_count}\r`); 
    // Output status of Completed / Total to the console without showing new lines
    // If all emails have completed validation
    if (completed == email_count) {
        const stop = window.performance.now(); // Stop the timer
        console.log(
            `All emails successfully validated in ${(stop - start) / 1000} seconds`
        );
    }
});