【Node.js】 Check tracking status. This code supports 349 couriers. Notify with Twitter.

app.js

/*
 * Notify tracking status with Twitter on Node.js.
 *
 * Usage
 * -------------------
 * node app.js "<tracking number>" "<your twitter username>"
 *
 * This code scraping 'track.aftership.com'
 */

const client = require('cheerio-httpcli');
const Twitter = require('twitter');
const fs = require('fs');

let flag = null;
let number = process.argv[2];
let user = process.argv[3];
let twitter = new Twitter({
    consumer_key: '',
    consumer_secret: '',
    access_token_key: '',
    access_token_secret: ''
});

/* check argument */
if (process.argv.length !== 4) {
    console.log('Missing argument. Please check argument.');
    process.exit();
}

/* check one before message file */
fs.stat('./latest', function (err, stat) {
    if (err == null) {
        flag = 0;

    } else if (err.code == 'ENOENT') {
        flag = 1;

    } else {
        process.exit('Error: ' + err.code);
    }
});

client.fetch('https://track.aftership.com/' + number, function (err, $, res) {
    let message = $('div.checkpoint__content strong').eq(0).text();
    let date = $('div.checkpoint__time strong').eq(0).text() + $('div.hint').eq(0).text();

    /* one before message exist === 0 */
    if (flag === 0) {

        fs.readFile('./latest', 'utf-8', function(err, data){
            /* If different from one before, Notify~ */
            if (data !== new Buffer(message).toString('base64')) {
                /* write file for comparing ? Do I should change from base64 to message === message? */
                fs.writeFile('./latest', new Buffer(message).toString('base64'), function (err) {
                    // No error handling
                });

                twitter.post('statuses/update', {
                    status: '@' + user + ' Number: ' + number + '\n' +
                    'Date: ' + date.replace(/\d{4}/g, "") + '\n' +
                    'Message: ' + message.slice(0, 40) + '...\n' +
                    'https://track.aftership.com/singapore-post/' + number

                }, function (error, tweet, response) {
                    // No error handling
                    console.log(response);
                });
            }
        });

    } else {
        /* write file for comparing ? Do I should change from base64 to message === message? */
        fs.writeFile('./latest', new Buffer(message).toString('base64'), function (err) {
            // No error handling
        });

        twitter.post('statuses/update', {
            status: '@' + user + ' Number: ' + number + '\n' +
            'Date: ' + date.replace(/\d{4}/g, "") + '\n' +
            'Message: ' + message.slice(0, 40) + '...\n' +
            'https://track.aftership.com/singapore-post/' + number

        }, function (error, tweet, response) {
            // No error handling
            console.log(response);
        });
    }
});