bot.js

const response_emoji = ['😭', '😢', '😞', '😐', '🙂', '😃', '😄'];

controller.on('direct_mention,direct_message', function(bot, message) {
  if(message.text) {
    const document = {
      content: message.text,
      type: 'PLAIN_TEXT',
    };

    client.analyzeSentiment({document: document})
      .then(results => {
        const sentiment = results[0].documentSentiment;
        
        if(sentiment.magnitude > 0.2) 
          bot.reply(message, `${response_emoji[Math.round(sentiment.score/.3) + 3]}`);
        else
          bot.reply(message, '😶');
      })
      .catch(err => {
        console.error('ERROR:', err);
      }); 
  }
});