app.js

const express = require('express');
const dialogflow = require('@google-cloud/dialogflow');
const uuid = require('uuid');
const cors = require('cors');

const app = express();

const sessionId = uuid.v4();

app.set('view engine','ejs');
app.use(express.static(__dirname + '/public'));



app.use(express.json())
app.use(express.urlencoded({ extended: false }));
app.use(cors());

//enabling CORS
app.use(function (req, res, next) {

    // Website you wish to allow to connect
    res.setHeader('Access-Control-Allow-Origin', '*');

    // Request methods you wish to allow
    res.setHeader('Access-Control-Allow-Methods', 'GET, POST, OPTIONS, PUT, PATCH, DELETE');

    // Request headers you wish to allow
    res.setHeader('Access-Control-Allow-Headers', 'X-Requested-With,content-type');

    // Set to true if you need the website to include cookies in the requests sent
    // to the API (e.g. in case you use sessions)
    res.setHeader('Access-Control-Allow-Credentials', true);

    // Pass to next layer of middleware
    next();
});

app.post('/send-msg', (req,res) =>{

    runSample(req.body.MSG).then(data =>{
        res.send({Reply: data})
    })
});

app.get('/',(req,res) => {
    res.render('index');
});

/**
 * Send a query to the dialogflow agent, and return the query result.
 * @param {string} projectId The project to be used
 */
async function runSample(MSG,projectId = 'rn-bot-lngc') {

  // Create a new session
  const sessionClient = new dialogflow.SessionsClient({
      //here have to change the path 
      keyFilename:"C:/Users/Parv/Desktop/ChatBot-NodeJs/key2.json",
  });
  const sessionPath = sessionClient.projectAgentSessionPath(
    projectId,
    sessionId
  );

  // The text query request.
  const request = {
    session: sessionPath,
    queryInput: {
      text: {
        // The query to send to the dialogflow agent
        text: MSG,
        // The language used by the client (en-US)
        languageCode: 'en-US',
      },
    },
  };

  // Send request and log result
  const responses = await sessionClient.detectIntent(request);
  console.log('Detected intent');
  const result = responses[0].queryResult;
  console.log(`  Query: ${result.queryText}`);
  console.log(`  Response: ${result.fulfillmentText}`);
  if (result.intent) {
    console.log(`  Intent: ${result.intent.displayName}`);
  } else {
    console.log('  No intent matched.');
  }
  return result.fulfillmentText;
}

app.listen(3000);