JavaScript TypeError ws

Всем привет! Не могу разобраться почему возникает эта ошибка в js:

router.ws('/', function (ws) { ^ TypeError: router.ws is not a function at new RealtimeServer (/Users/workspace/openmct/realtime-server.js:7:12)

Сам скрипт вот:

var express = require('express');

function RealtimeServer(spacecraft) {
    
    var router = express.Router();

    router.ws('/', function (ws) {
        var unlisten = spacecraft.listen(notifySubscribers);
        var subscribed = {}; // Active subscriptions for this connection
        var handlers = { // Handlers for specific requests
                subscribe: function (id) {
                    subscribed[id] = true;
                },
                unsubscribe: function (id) {
                    delete subscribed[id];
                }
            };

        function notifySubscribers(point) {
            if (subscribed[point.id]) {
                ws.send(JSON.stringify(point));
            }
        }

        // Listen for requests
        ws.on('message', function (message) {
            var parts = message.split(' '),
                handler = handlers[parts[0]];
            if (handler) {
                handler.apply(handlers, parts.slice(1));
            }
        });

        // Stop sending telemetry updates for this connection when closed
        ws.on('close', unlisten);
    });

    return router;
};

module.exports = RealtimeServer;