process-message.js

const projectId = '<your dialogflow project id>';
const sessionId = '123456';
const languageCode = 'en-US';

const dialogflow = require('dialogflow');

const config = {
  credentials: {
    private_key: process.env.DIALOGFLOW_PRIVATE_KEY,
    client_email: process.env.DIALOGFLOW_CLIENT_EMAIL,
  },
};

const sessionClient = new dialogflow.SessionsClient(config);

const sessionPath = sessionClient.sessionPath(projectId, sessionId);

module.exports = async event => {
  const message = event.message.text;

  const request = {
    session: sessionPath,
    queryInput: {
      text: {
        text: message,
        languageCode: languageCode,
      },
    },
  };

  const responses = await sessionClient.detectIntent(request);
  const result = responses[0].queryResult;
  return result;
};