a.js

var keyFile           = 'keys/' + config.bot.username + '.key';

fs.readFile('polldata.json', function (err, data) {
    if (err) {
        logger.warn('Error reading polldata.json');
    } else {
        logger.debug('Importing previous tradeoffer data');
        offers.pollData = JSON.parse(data);
    }
});

fs.readFile(keyFile, function (err, data) {
    var loginKey = null;
    if (!err) {
        loginKey = data;
        console.log('Found loginKey: ' + loginKey);
    }

    // Login into steam
    client.logOn({
        accountName: config.bot.username,
        password: config.bot.password,
        rememberPassword: true,
        loginKey: loginKey
    });
});

client.on('loginKey', function (key) {
    console.log('Got key: ' + key);
    fs.writeFile(keyFile, key);
});