Injecting a Data Service in a React App - DAV-1000/react-material GitHub Wiki

Created: 8/4/2025 16:28
Updated: 8/4/2025 17:41
Exported: 8/14/2025 11:43
Link: https://chatgpt.com/c/6890d1ad-ce5c-8001-aa39-a599142dc932

How do i inject a data service into a react page

Injecting a data service into a React page is usually done using one of the following approaches, depending on how you’ve structured your application and what kind of data service it is (e.g., REST API wrapper, Firebase, GraphQL client, etc.).

Here’s a clean and modern way using Context API and React hooks, which keeps your code modular, testable, and maintainable.

This could be an API wrapper or any object that performs data fetching:

// services/apiService.js
export const apiService = {
  getUsers: async () => {
    const response = await fetch('/api/users');
    if (!response.ok) throw new Error('Failed to fetch users');
    return await response.json();
  },
  // other API methods...
};

// contexts/ApiServiceContext.js
import React, { createContext, useContext } from 'react';
import { apiService } from '../services/apiService';

const ApiServiceContext = createContext();

export const ApiServiceProvider = ({ children }) => {
  return (
    <ApiServiceContext.Provider value={apiService}>
      {children}
    </ApiServiceContext.Provider>
  );
};

export const useApiService = () => useContext(ApiServiceContext);

// App.jsx or your page component
import React from 'react';
import { ApiServiceProvider } from './contexts/ApiServiceContext';
import HomePage from './pages/HomePage';

const App = () => (
  <ApiServiceProvider>
    <HomePage />
  </ApiServiceProvider>
);

export default App;

// pages/HomePage.jsx
import React, { useEffect, useState } from 'react';
import { useApiService } from '../contexts/ApiServiceContext';

const HomePage = () => {
  const api = useApiService();
  const [users, setUsers] = useState([]);

  useEffect(() => {
    api.getUsers()
      .then(setUsers)
      .catch(console.error);
  }, [api]);

  return (
    <div>
      <h1>Users</h1>
      <ul>
        {users.map(u => (
          <li key={u.id}>{u.name}</li>
        ))}
      </ul>
    </div>
  );
};

export default HomePage;

• Dependency injection via props — for small apps or testing purposes.
• Using external state libraries — like Redux Toolkit Query or React Query.
• Using custom hooks — to encapsulate service logic more tightly.

Would you like an example using React Query or Axios instead?

Use typescript please

Sure! Here's the TypeScript version of injecting a data service into a React page using Context API and custom hooks.

// services/ApiService.ts
export interface User {
  id: number;
  name: string;
}

export interface ApiService {
  getUsers: () => Promise<User[]>;
}

export const apiService: ApiService = {
  getUsers: async () => {
    const response = await fetch('/api/users');
    if (!response.ok) {
      throw new Error('Failed to fetch users');
    }
    return await response.json();
  },
};

// contexts/ApiServiceContext.tsx
import React, { createContext, useContext } from 'react';
import { apiService, ApiService } from '../services/ApiService';

const ApiServiceContext = createContext<ApiService | null>(null);

export const ApiServiceProvider: React.FC<{ children: React.ReactNode }> = ({ children }) => {
  return (
    <ApiServiceContext.Provider value={apiService}>
      {children}
    </ApiServiceContext.Provider>
  );
};

export const useApiService = (): ApiService => {
  const context = useContext(ApiServiceContext);
  if (!context) {
    throw new Error('useApiService must be used within an ApiServiceProvider');
  }
  return context;
};

// App.tsx
import React from 'react';
import { ApiServiceProvider } from './contexts/ApiServiceContext';
import HomePage from './pages/HomePage';

const App: React.FC = () => {
  return (
    <ApiServiceProvider>
      <HomePage />
    </ApiServiceProvider>
  );
};

export default App;

// pages/HomePage.tsx
import React, { useEffect, useState } from 'react';
import { useApiService } from '../contexts/ApiServiceContext';
import { User } from '../services/ApiService';

const HomePage: React.FC = () => {
  const api = useApiService();
  const [users, setUsers] = useState<User[]>([]);
  const [loading, setLoading] = useState<boolean>(true);
  const [error, setError] = useState<string | null>(null);

  useEffect(() => {
    api.getUsers()
      .then(setUsers)
      .catch(err => setError(err.message))
      .finally(() => setLoading(false));
  }, [api]);

  if (loading) return <div>Loading...</div>;
  if (error) return <div>Error: {error}</div>;

  return (
    <div>
      <h1>Users</h1>
      <ul>
        {users.map(u => (
          <li key={u.id}>{u.name}</li>
        ))}
      </ul>
    </div>
  );
};

export default HomePage;

• Full TypeScript safety across services and consumers.
• Easy to mock ApiService for unit testing.
• Decouples your component logic from your data access layer.

Let me know if you'd like to use this pattern with Axios, React Query, or Dependency Injection frameworks like inversify.

In React 19, use is preferred over useContext because it is more flexible.

You're absolutely right — in React 19, the use() hook (introduced in React 18.3+ with the React Compiler) is indeed the preferred way to access asynchronous or context-based dependencies, especially for data loading in Server Components (RSC) or using async contexts.

Let me show you how to rewrite the previous data service injection example using the React 19 use() hook pattern.

⚠️ use() can only be used in async Server Components. It does not work in traditional Client Components.

// services/ApiService.ts
export interface User {
  id: number;
  name: string;
}

export interface ApiService {
  getUsers: () => Promise<User[]>;
}

export const apiService: ApiService = {
  getUsers: async () => {
    const response = await fetch('https://jsonplaceholder.typicode.com/users');
    if (!response.ok) throw new Error('Failed to fetch users');
    return await response.json();
  },
};

// contexts/ApiServiceContext.tsx
import { createContext } from 'react';
import { apiService, ApiService } from '../services/ApiService';

export const ApiServiceContext = createContext<ApiService>(apiService);

This works because use() can unwrap context values automatically in server components.

// app/pages/HomePage.tsx (React Server Component)
'use server';

import { use } from 'react';
import { ApiServiceContext } from '../contexts/ApiServiceContext';

const HomePage = async () => {
  const api = use(ApiServiceContext); // Unwrap the service
  const users = await api.getUsers(); // Server-side data fetching

  return (
    <div>
      <h1>Users (Server Component)</h1>
      <ul>
        {users.map((u) => (
          <li key={u.id}>{u.name}</li>
        ))}
      </ul>
    </div>
  );
};

export default HomePage;

• The new use() hook allows consuming context and Promises directly in Server Components.
• Contexts no longer need wrapping useContext() in Client Components when used with use() in the server.
• Works with the React Compiler to optimize tree-shaking, caching, and re-rendering.

Let me know if you want a hybrid setup: Server Component using use() + Client Components for interactivity.

My page uses React.useState which cannot be used in an async funciton

Exactly — you're running into a key limitation in React 19: useState() (and other client-only hooks like useEffect, useRef, etc.) cannot be used in async Server Components.

If you write:

const HomePage = async () => {
  const [users, setUsers] = React.useState([]); // ❌ Invalid in async components
  // ...
};

This fails because useState is a client-only hook, while async components are treated as server components.

In React 19, the proper pattern is to:

1. Fetch data in a Server Component using use() or an async function.
2. Pass the result to a Client Component that handles interactivity (useState, useEffect, etc.).

// app/pages/HomePage.tsx
'use server';

import { use } from 'react';
import { ApiServiceContext } from '../contexts/ApiServiceContext';
import { UserList } from '../components/UserList';

const HomePage = async () => {
  const api = use(ApiServiceContext);
  const users = await api.getUsers();

  return <UserList initialUsers={users} />;
};

export default HomePage;

// components/UserList.tsx
'use client';

import React, { useState } from 'react';
import { User } from '../services/ApiService';

interface Props {
  initialUsers: User[];
}

export const UserList: React.FC<Props> = ({ initialUsers }) => {
  const [users, setUsers] = useState<User[]>(initialUsers);

  return (
    <div>
      <h1>Users (Client Component)</h1>
      <ul>
        {users.map((u) => (
          <li key={u.id}>{u.name}</li>
        ))}
      </ul>
    </div>
  );
};

Let me know if you'd like to refactor an existing page, or need data revalidation, pagination, or optimistic UI added to this pattern.

Will a server component run in a static web app

Great question — and the short answer is:

No, Server Components do not run in a static web app.

A static web app (like those deployed via Netlify static hosting, GitHub Pages, or Vercel static export) can only serve prebuilt HTML and static assets. It doesn't have a backend runtime, so it can't run Server Components, which rely on the server to:

• Access context via use()
• Run async logic (e.g., database or API fetches)
• Stream React output to the client

You’re limited to Client Components and Static Site Generation (SSG). This means:

• You can fetch data at build time using something like getStaticProps() (Next.js) or prerender APIs
• You must do dynamic data fetching on the client using useEffect or a library like React Query
• You cannot use the new React 19 use() hook unless your app is deployed to a server-capable platform

You'll need to deploy to a platform that supports server-side React rendering, such as:

• Vercel (with Next.js App Router)
• Netlify Edge Functions (for SSR)
• Cloudflare Pages (with Functions)
• Node.js-based backend (Express, etc.)

These platforms run your Server Components at request time and stream the result to the browser.

If you're using a specific framework (like Next.js, Remix, or Vite), I can tailor the answer to that context. Want help adapting to static-only constraints or picking a hosting strategy?

I want to use the service in my home page which is identified in App.tsx as a rote: <Route path="/" element={} /> what is the syntax for this

Thanks — you're working with React Router in a Client Component–only app, likely with react-router-dom, and you want to use a data service like apiService in your <Home /> page.

Since this is a fully client-rendered setup, you cannot use async components or use() — instead, you'll:

1. Inject your service via a React Context (optional, but clean).
2. Use it in your page with useEffect() and useState().

// App.tsx
import { BrowserRouter, Routes, Route } from 'react-router-dom';
import { ApiServiceProvider } from './contexts/ApiServiceContext';
import Home from './pages/Home';

function App() {
  return (
    <ApiServiceProvider>
      <BrowserRouter>
        <Routes>
          <Route path="/" element={<Home />} />
        </Routes>
      </BrowserRouter>
    </ApiServiceProvider>
  );
}

export default App;

// contexts/ApiServiceContext.tsx
import React, { createContext, useContext } from 'react';
import { apiService, ApiService } from '../services/ApiService';

const ApiServiceContext = createContext<ApiService | null>(null);

export const ApiServiceProvider: React.FC<{ children: React.ReactNode }> = ({ children }) => (
  <ApiServiceContext.Provider value={apiService}>
    {children}
  </ApiServiceContext.Provider>
);

export const useApiService = (): ApiService => {
  const context = useContext(ApiServiceContext);
  if (!context) {
    throw new Error('useApiService must be used inside ApiServiceProvider');
  }
  return context;
};

// pages/Home.tsx
import React, { useEffect, useState } from 'react';
import { useApiService } from '../contexts/ApiServiceContext';
import { User } from '../services/ApiService';

const Home: React.FC = () => {
  const api = useApiService();
  const [users, setUsers] = useState<User[]>([]);
  const [loading, setLoading] = useState(true);
  const [error, setError] = useState<string | null>(null);

  useEffect(() => {
    api.getUsers()
      .then(setUsers)
      .catch((err) => setError(err.message))
      .finally(() => setLoading(false));
  }, [api]);

  if (loading) return <div>Loading users...</div>;
  if (error) return <div>Error: {error}</div>;

  return (
    <div>
      <h1>Users</h1>
      <ul>
        {users.map(u => (
          <li key={u.id}>{u.name}</li>
        ))}
      </ul>
    </div>
  );
};

export default Home;

This structure ensures:

• Fully client-side routing with <Route path="/" element={<Home />} />
• Clean separation of data logic using a context
• Compatibility with any static or client-only deployment

Let me know if you'd like:

• To inject different service implementations (e.g., mock vs. real)?
• To add loading skeletons or pagination?
• To use a custom hook like useUsers() instead?

Happy to help build it out.

In this code block, children implicitly has an 'any' type export const ApiServiceProvider = ({ children }) => { return ( <ApiServiceContext.Provider value={apiService}> {children} </ApiServiceContext.Provider> ); };

Great catch — you're seeing this because TypeScript doesn't know the type of children, and you're not explicitly typing the props.

To fix this, you need to annotate the children prop using React.PropsWithChildren, or explicitly declare the type of the props object.

Here are two clean ways to do it.

import React from 'react';

export const ApiServiceProvider: React.FC = ({ children }) => {
  return (
    <ApiServiceContext.Provider value={apiService}>
      {children}
    </ApiServiceContext.Provider>
  );
};

This works because React.FC automatically includes children?: React.ReactNode.

import React, { PropsWithChildren } from 'react';

export const ApiServiceProvider = ({ children }: PropsWithChildren<{}>) => {
  return (
    <ApiServiceContext.Provider value={apiService}>
      {children}
    </ApiServiceContext.Provider>
  );
};

This is more explicit and sometimes preferred in larger apps where you want full control over the props.

Avoid leaving it untyped — that's what causes the 'any' type warning. And don't use any unless you have to.

Let me know if you’d like to strongly type the context itself for auto-complete and safety in useContext().

Can I not just declare the type of children

Yes, absolutely — you can directly declare the type of children without using React.FC or PropsWithChildren if you prefer being explicit.

Here’s how to do it cleanly:

import React from 'react';

type ApiServiceProviderProps = {
  children: React.ReactNode;
};

export const ApiServiceProvider = ({ children }: ApiServiceProviderProps) => {
  return (
    <ApiServiceContext.Provider value={apiService}>
      {children}
    </ApiServiceContext.Provider>
  );
};

This works perfectly, keeps your code explicit, and avoids the any type warning. It's also more flexible and clearer than using React.FC if you want to control which props are allowed.

Let me know if you'd like to also type the context value itself for full IntelliSense inside useApiService().

When I debug it, the call to setUsers in this code block throws an error. How can I see what is being passed to the method: useEffect(() => { api.getUsers() .then(setUsers) .catch((err) => setError(err.message)) .finally(() => setLoading(false)); }, [api]);

Good question — when setUsers() throws, it usually means something unexpected (like undefined, a string, or malformed data) is being passed into it. To debug that precisely:

Replace the .then(setUsers) with an explicit function that logs the value:

useEffect(() => {
  api.getUsers()
    .then((users) => {
      console.log('Fetched users:', users); // ✅ See what you're passing to setUsers
      setUsers(users);
    })
    .catch((err) => {
      console.error('Error fetching users:', err); // ✅ Inspect the actual error
      setError(err.message);
    })
    .finally(() => setLoading(false));
}, [api]);

This gives you full visibility into:

• What getUsers() is returning
• Whether it’s an array as expected
• Any unexpected shape or error

If your users state is typed like this:

const [users, setUsers] = useState<User[]>([]);

Then passing anything other than an array of User will throw at runtime in some strict setups or crash your rendering (especially in lists like users.map()).

You’ll see it in the console.log. A common fix is to validate it:

.then((users) => {
  if (!Array.isArray(users)) {
    throw new Error('Expected an array of users');
  }
  setUsers(users);
})

function isUserArray(data: unknown): data is User[] {
  return Array.isArray(data) && data.every(u => typeof u.id === 'number' && typeof u.name === 'string');
}

Then:

.then((data) => {
  if (!isUserArray(data)) {
    throw new Error('Invalid user data format');
  }
  setUsers(data);
})

Would you like help writing a testable mock of api.getUsers() or debugging an actual error message from your console?

My service retrieves the json data as below but what is returned from the npm dev server is the index page: export const blogPostService: BlogPostService = { getAll: async () => { const response = await fetch('/data/cardData.json'); if (!response.ok) { throw new Error('Failed to fetch posts'); } console.log(response); console.log('Response status:', response.status); console.log('Response headers:', response.headers); console.log('Response body:', await response.text()); return await response.json(); }, };

Ah — this is a very common issue when using fetch('/data/cardData.json') in a React app served via an npm dev server (like Vite, CRA, or Next.js dev).

When you fetch /data/cardData.json:

• The browser makes a request to http://localhost:3000/data/cardData.json (or wherever you're running your app).
• If that file doesn't exist in the public/static assets, the dev server falls back to serving the index.html page (as part of SPA routing).
• So instead of JSON, you're getting an HTML file, which causes await response.json() to throw, or response.text() to show your whole index page.

You need to ensure the JSON file is accessible as a static asset.

Place cardData.json in the public folder:

/public
  └── /data
      └── cardData.json

Then fetch it with:

fetch('/data/cardData.json')

✅ This will work — anything in public/ is served as-is.

Same as above — place the JSON in public/data/cardData.json, not in src.

Then fetch it with the same path:

fetch('/data/cardData.json')

Put the file in public/data/cardData.json. Then access it from /data/cardData.json.

✅ public/ in Next.js is available at the root path during dev and build.

Right-click → "Open in new tab" on the file at:
http://localhost:3000/data/cardData.json
If you get your HTML app page, not JSON → it's being routed incorrectly or the file isn’t there.

To debug more gracefully:

const response = await fetch('/data/cardData.json');

if (!response.ok) {
  const errorText = await response.text();
  console.error('Failed to fetch JSON:', errorText);
  throw new Error('Failed to fetch posts');
}

const contentType = response.headers.get('content-type');
if (!contentType?.includes('application/json')) {
  const text = await response.text();
  throw new Error('Expected JSON but got: ' + text.slice(0, 100));
}

const data = await response.json();
return data;

Let me know your specific setup (Vite, CRA, Next.js, etc.), and I can give you the exact folder structure or even a dev server mock if needed.

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