What can replace FileReader in react?

Question

JavaScript

I am rewriting js code in react native. Everything works for me, only there is no file reader in react. It shows that everything is connected, but throws an error after onmessage...

reader = new FileReader();
reader.onload = function() {
    alert(reader.result);
}
var socket = new WebSocket("ws://77.87.917.23:8023", 'binary');
socket.onopen = function() {
  alert("Соединение установлено.");
};
socket.onclose = function(event) {
  if (event.wasClean) {
    alert('Соединение закрыто чисто');
  } else {
    alert('Обрыв соединения'); // например, "убит" процесс сервера
  }
  alert('Код: ' + event.code + ' причина: ' + event.reason);
};
socket.onmessage = function(event) {
  reader.readAsText(event.data);
};