How to use @grpc/grpc-js

/**
  * Creates a new ContractRegistry instance
  *
  * @param endpoint - the URL and port of the contract registry RPC
  * @param options - optional gRPC channel options
  */
 constructor(endpoint: string, options?: ChannelOptions) {
  this.rpcClient = new Client(endpoint, ChannelCredentials.createInsecure(), options)
 }

/**
  * Initialize grpc-node clients for each rpc service, lazy connection under the surface
  *
  * @private
  */
 _initRpcClients() {
  const socket = this._endpoint.split('//').pop();
  this.clients = Object.keys(rpcs).reduce((acc, x) => {
   debug('initRpcClient', x);
   acc[x] = new rpcs[x](socket, grpc.credentials.createInsecure());
   return acc;
  }, {});
 }

private rpc(method: string, requestData: Buffer, callback: UnaryCallback<Buffer>, authToken?: string) {
  const serializeF = (request: Buffer) => request
  const deSerializeF = (response: Buffer) => response

  const metadata = new Metadata()
  if (authToken) {
   metadata.set('Authorization', authToken)
  }

  this.rpcClient.makeUnaryRequest(
   `contractregistry.ContractRegistry/${method}`,
   serializeF,
   deSerializeF,
   requestData,
   metadata,
   callback
  )
 }