server.js

/* Setting things up. */
var fs = require('fs'),
    path = require('path'),
    express = require('express'),
    app = express(),   
    Twit = require('twit'),
    config = {
    /* Be sure to update the .env file with your API keys. See how to get them: https://botwiki.org/tutorials/make-an-image-posting-twitter-bot/#creating-a-twitter-app*/      
      twitter: {
        consumer_key: process.env.CONSUMER_KEY,
        consumer_secret: process.env.CONSUMER_SECRET,
        access_token: process.env.ACCESS_TOKEN,
        access_token_secret: process.env.ACCESS_TOKEN_SECRET
      }
    },
    T = new Twit(config.twitter),
    stream = T.stream('statuses/sample');

var bot_responses = [
  "I am awake!",
  "I'm awake!",
  "I dozed off.",
  "I dozed off, but I am awake now!",
  "I dozed off, but I'm awake now!"
];

function random_from_array(arr){
  return arr[Math.floor(Math.random()*arr.length)]; 
}

app.use(express.static('public'));

/* You can use uptimerobot.com or a similar site to hit your /tweet endpoint to wake up your app and make your Twitter bot tweet. */

app.all("/tweet", function (request, response) {
  /* Respond to @ mentions */
  fs.readFile(__dirname + '/last_mention_id.txt', 'utf8', function (err, last_mention_id) {
    /* First, let's load the ID of the last tweet we responded to. */
    console.log('last_mention_id:', last_mention_id);

    T.get('search/tweets', { q: 'to:' + process.env.TWITTER_HANDLE + ' -from:' + process.env.TWITTER_HANDLE, since_id: last_mention_id }, function(err, data, response) {
      if (err){
        console.log('Error!', err);
        return false;
      }
      /* Next, let's search for Tweets that mention our bot, starting after the last mention we responded to. */
      if (data.statuses.length){
        // console.log(data.statuses);
        data.statuses.forEach(function(status) {
          console.log(status.id_str);
          console.log(status.text);
          console.log(status.user.screen_name);

          /* Now we can respond to each tweet. */
          T.post('statuses/update', {
            status: '@' + status.user.screen_name + ' ' + random_from_array(bot_responses),
            in_reply_to_status_id: status.id_str
          }, function(err, data, response) {
            if (err){
                /* TODO: Proper error handling? */
              console.log('Error!', err);
            }
            else{
              fs.writeFile(__dirname + '/last_mention_id.txt', status.id_str, function (err) {
                /* TODO: Error handling? */
                if(err){
                  console.log('Error!', err);
                }
              });
            }
          });
        });
      } else {
        /* No new mentions since the last time we checked. */
        console.log('No new mentions...');      
      }
    });    
  });

  /* Respond to DMs */

  fs.readFile(__dirname + '/last_dm_id.txt', 'utf8', function (err, last_dm_id) {
    if (err){
      console.log('Error!', err);
      return false;
    }
    /* Load the ID of the last DM we responded to. */
    console.log('last_dm_id:', last_dm_id);

    T.get('direct_messages', { since_id: last_dm_id, count: 200 }, function(err, dms, response) {
      /* Next, let's search for Tweets that mention our bot, starting after the last mention we responded to. */
      if (dms.length){
        dms.forEach(function(dm) {
          console.log(dm.sender_id);
          console.log(dm.id_str);
          console.log(dm.text);

          /* Now we can respond to each tweet. */
          T.post('direct_messages/new', {
            user_id: dm.sender_id,
            text: random_from_array(bot_responses)
          }, function(err, data, response) {
            if (err){
              /* TODO: Proper error handling? */
              console.log('Error!');
              console.log(err);
            }
            else{
              fs.writeFile(__dirname + '/last_dm_id.txt', dm.id_str, function (err) {
                /* TODO: Error handling? */
              });
            }
          });
        });
      } else {
        /* No new DMs since the last time we checked. */
        console.log('No new DMs...');      
      }
    });    
  });  
  
  /* TODO: Handle proper responses based on whether the tweets succeed, using Promises. For now, let's just return a success message no matter what. */
  response.sendStatus(200);
});

var listener = app.listen(process.env.PORT, function () {
  console.log('Your bot is running on port ' + listener.address().port);
});