Uncaught TypeError: WebSocketServer is not a constructor about rpc-websockets HOT 1 CLOSED

var WebSocket = require('rpc-websockets').Client
var WebSocketServer = require('rpc-websockets').Server

// instantiate Server and start listening for requests
var server = new WebSocketServer({
  port: 8080,
  host: 'localhost'
})

server.register('feedUpdated', function(p, s) {
    console.log('msg rcvd from:', s)
})

server.register('secret', function(p, s) {
    console.log('secret msg rcvd from:', s)
}).protected()

server.setAuth(() => {
    console.log('logged in')
    return true
})

nr = '12345678'

const main = async() => {
    var ws = new WebSocket('ws://localhost:8080?socket_id=' + nr)

    ws.on('open', async function() {
        await ws.notify('feedUpdated')

        await ws.login({'username': 'confi1', 'password':'foobar'})

        try {
            await ws.call('secret')
            console.log('ws ok')
        } catch (err) {
            console.log(err)
        }
    })

    var wsu = new WebSocket('ws://localhost:8080?socket_id=9999')

    wsu.on('open', async function() {
        try {
            await wsu.call('secret')
        } catch (err) {
            console.log('wsu', err)
        }
    })
}

main()