Concurrent Mode Suspense example

concurrent-mode-suspense.js

/**
 * The issues I found are the following:
 * 1) No 'fallback', the benefit of suspense is to render as early as possible.
 * 2) The component fetching the data should "suspend", fetching user profile in a useEffect
 * Doesn't do that.
 * 3) The suspense should wrap the componenet fetching the data (i.e. SuspensefulUserProfile).
 *
 * Extra notes:
 * - Making a request for each profile separately is definitely something to be avoided,
 * it would be much better to fetch the profiles together.
 * - No error handling. The way to handle errors in this case is by adding an ErrorBounary.
 * - Relay should be used in this case since Suspense on it's own is not ready, yet.
 */


import { Suspense, Component } from "react";
import { fetchProfileData } from "./fetchUser"

const SuspensefulUserProfile = ({ userId }) => {
  const data = fetchProfileData(userId).read();
  return <UserProfile data={data} />;
};


const UserProfile = ({ data }) => {
  return (
    <>
      <h1>{data.name}</h1>
      <h2>{data.email}</h2>
    </>
  );
};

const UserProfileList = () => (
  <>
    <ErrorBoundary fallback={<UserProfileError />}>
      <Suspense fallback={<UserProfileLoading />}>
        <SuspensefulUserProfile userId={1} />
      </Suspense>
    </ErrorBoundary>
    <ErrorBoundary fallback={<UserProfileError />}>
      <Suspense fallback={<UserProfileLoading />}>
        <SuspensefulUserProfile userId={2} />
      </Suspense>
    </ErrorBoundary>
    <ErrorBoundary fallback={<UserProfileError />}>
      <Suspense fallback={<UserProfileLoading />}>
        <SuspensefulUserProfile userId={3} />
      </Suspense>
    </ErrorBoundary>
  </>
);


class ErrorBoundary extends Component {
  state = { hasError: false, error: null };
  static getDerivedStateFromError(error) {
    return {
      hasError: true,
      error
    };
  }
  render() {
    if (this.state.hasError) {
      return this.props.fallback;
    }
    return this.props.children;
  }
}

const UserProfileLoading = () => {
  return <div>Loading user profile...</div>;
};

const UserProfileError = () => {
  return <div>Failed to fetch user list</div>;
};

fetchUser.js

const users = {
  1: {
    name: "John",
    email: "[email protected]"
  },
  2: {
    name: "eric",
    email: "[email protected]"
  },
  3: {
    name: "hamza",
    email: "[email protected]"
  }
};

/**
 * Api call to fetch user profile
 */
const fetchUserProfile = (userId) => {
  if (users[userId]) {
    return Promise.resolve(() => users[userId]);
  }
  return Promise.reject(() => new Error("User profile not found."));
};

/**
 * Suspending api call to fetch user profile
 */
const fetchUserProfileData = (userId) => {
  return wrapPromise(fetchUserProfile(userId));
};





// Suspense integrations like Relay implement
// a contract like this to integrate with React.
// This code is copied from react suspense docs (not intended for prod).
// check here: https://codesandbox.io/s/frosty-hermann-bztrp?file=/src/index.js
function wrapPromise(promise) {
  let status = "pending";
  let result;
  let suspender = promise.then(
    (r) => {
      status = "success";
      result = r;
    },
    (e) => {
      status = "error";
      result = e;
    }
  );
  return {
    read() {
      if (status === "pending") {
        throw suspender;
      } else if (status === "error") {
        throw result;
      } else if (status === "success") {
        return result;
      }
    }
  };
}