Why am i getting this error: TypeError: undefined is not a function

[CrispenGari]

I'm using urql and react-native because i'm in love with it as a graphql-client. Here is how I'm creating a client:

import React from "react";
import {
  Client,
  Provider,
  cacheExchange,
  fetchExchange,
  subscriptionExchange,
} from "urql";
import { KEYS, serverDomain } from "../constants";
import { del, retrieve } from "../utils";
import { createClient as createSSEClient } from "graphql-sse";
import { authExchange } from "@urql/exchange-auth";
interface Props {
  children: React.ReactNode;
}

const sseClient = createSSEClient({
  url: `http://${serverDomain}/graphql`,
});
const client = new Client({
  url: `http://${serverDomain}/graphql`,
  requestPolicy: "network-only",
  exchanges: [
    cacheExchange,
    authExchange(async (utils) => {
      const jwt = await retrieve(KEYS.TOKEN_KEY);

      return {
        addAuthToOperation(operation) {
          if (jwt) {
            return utils.appendHeaders(operation, {
              Authorization: `Bearer ${jwt}`,
            });
          }
          return operation;
        },
        willAuthError(_operation) {
          return !jwt;
        },
        didAuthError(error, _operation) {
          return error.graphQLErrors.some(
            (e) => e.extensions?.code === "FORBIDDEN"
          );
        },
        async refreshAuth() {
          await del(KEYS.TOKEN_KEY);
        },
      };
    }),
    fetchExchange,
    subscriptionExchange({
      forwardSubscription(operation) {
        return {
          subscribe: (sink) => {
            const dispose = sseClient.subscribe(operation as any, sink);
            return {
              unsubscribe: dispose,
            };
          },
        };
      },
    }),
  ],
});
const UrqlProvider: React.FunctionComponent<Props> = ({ children }) => {
  return <Provider value={client}>{children}</Provider>;
};

export default UrqlProvider;

If I try to make a query or mutation to the server i get the error saying:

TypeError: undefined is not a function.

But if i comment the fetchExchange and refresh then the error goes away but i can't make mutations anymore. What may be posibly the issue with my exchanges here, Does the order of exchanges maters. Any ideas that can help me out here??

[CrispenGari]

I managed to solve my issue by dong the following.

1. install core-js

yarn add core-js

Then add the following import at the top in the root component of my app:

import 'core-js/full/symbol/async-iterator';