How to use the @line/bot-sdk.middleware function in @line/bot-sdk

// create LINE SDK client
const client = new line.Client(config);

// create Express app
// about Express itself: https://expressjs.com/
const app = express();

// serve static and downloaded files
app.use('/static', express.static('static'));
app.use('/downloaded', express.static('downloaded'));

app.get('/callback', (req, res) => res.end(`I'm listening. Please access with POST.`));

// webhook callback
app.post('/callback', line.middleware(config), (req, res) => {
  if (req.body.destination) {
    console.log("Destination User ID: " + req.body.destination);
  }

  // req.body.events should be an array of events
  if (!Array.isArray(req.body.events)) {
    return res.status(500).end();
  }

  // handle events separately
  Promise.all(req.body.events.map(handleEvent))
    .then(() => res.end())
    .catch((err) => {
      console.error(err);
      res.status(500).end();
    });

// create LINE SDK config from env variables
const config = {
    channelAccessToken: process.env.CHANNEL_ACCESS_TOKEN,
    channelSecret: process.env.CHANNEL_SECRET,
};

// create LINE SDK client
const client = new line.Client(config);

// create Express app
// about Express itself: https://expressjs.com/
const app = express();

// register a webhook handler with middleware
// about the middleware, please refer to doc
app.post('/', line.middleware(config), (req, res) => {
    Promise
        .all(req.body.events.map(handleEvent))
        .then((result) => res.json(result));
});

// event handler
function handleEvent(event) {
    if (event.type !== 'message' || event.message.type !== 'text') {
        // ignore non-text-message event
        return Promise.resolve(null);
    }

    var options1 = {
        method: 'GET',
        url: 'http://api.susi.ai/susi/chat.json',
        qs: {

// create LINE SDK config from env variables
const config = {
  channelAccessToken: process.env.CHANNEL_ACCESS_TOKEN,
  channelSecret: process.env.CHANNEL_SECRET,
};

// create LINE SDK client
const client = new line.Client(config);

// create Express app
// about Express itself: https://expressjs.com/
const app = express();

// register a webhook handler with middleware
// about the middleware, please refer to doc
app.post('/callback', line.middleware(config), (req, res) => {
  Promise
    .all(req.body.events.map(handleEvent))
    .then((result) => res.json(result));
});

// event handler
function handleEvent(event) {
  if (event.type !== 'message' || event.message.type !== 'text') {
    // ignore non-text-message event
    return Promise.resolve(null);
  }

  // create a echoing text message
  const echo = { type: 'text', text: event.message.text };

  // use reply API

app.post('/webhook', (req, res, next) => {
  const lineConfig = getLineConfig(req)
  middleware(lineConfig)(req, res, async err => {
    if (err) return next(err)
    endpoint(async (context, req, services) => {
      const client = services.line
      const data = await handleWebhook(context, req.body.events, client)
      console.log('Response:', data)
      return data
    })(req, res, next)
  })
})

require('dotenv').config();

const express = require('express');
const line = require('@line/bot-sdk');

const webhookHandler = require('./handler/webhook');
const healthyCheckHandler = require('./handler/healthy-check');
const config = require('./config.js');

const app = express();

app.get('/', healthyCheckHandler);

app.post('/webhook', line.middleware(config), webhookHandler);

app.listen(process.env.PORT || 3000);