ReferenceError: Pusher is not defined

Question

enter image description here Websocket can run well but there is still an error, namely Reference Pusher is not defined, what should I do.

export const echoInstance = new Echo({
  broadcaster: "pusher",
  key: process.env.PUSHER_APP_KEY,
  wsHost: process.env.PUSHER_HOST,
  wsPort:  process.env.PUSHER_PORT,
  forceTLS: true,
  disableStats: true,
  encrypted: true,
  cluster:  process.env.PUSHER_APP_CLUSTER,
  authEndpoint:  process.env.PUSHER_AUTH_ENDPOINT,
  auth: {
    headers: {
      Accept: "application/json",
      Authorization:
      `Bearer ${existingToken}`,
    },
  },
  enabledTransports: ['ws', 'wss'],
});