⚡ React–FastAPI Integration

A beginner-friendly guide to connecting your frontend (React) with your backend (FastAPI).

🧠 Why React + FastAPI?

React builds interactive UIs, while FastAPI provides fast and reliable APIs.
Together, they form a powerful full-stack setup:

• FastAPI handles data and authentication
• React handles user experience and interaction

This guide covers:

1. API Client Setup
2. CRUD Operations
3. State Synchronization
4. Error Boundaries

Each explained simply with short code and real-world examples.

⚙️ 1. API Client Setup

🔹 The Concept

Instead of using fetch() in every component, it’s better to create one API client that handles all communication between React and FastAPI.

This keeps the code organized, clean, and reusable.

🔹 Example

// apiClient.js
import axios from "axios";

const apiClient = axios.create({
  baseURL: "http://127.0.0.1:8000",
  headers: { "Content-Type": "application/json" },
});

export default apiClient;

Now this client can call any FastAPI endpoint.

💡 Real-World Example: Just like a restaurant waiter communicates between customers and the kitchen — your apiClient acts as a messenger between React (frontend) and FastAPI (backend).

🔹 Benefits

🧱 2. CRUD Operations

CRUD means Create, Read, Update, Delete — the core actions for any data-driven app.

🔹 FastAPI Example (Backend)

# main.py
from fastapi import FastAPI
app = FastAPI()

tasks = []

@app.get("/tasks")
def get_tasks():
    return tasks

@app.post("/tasks")
def add_task(task: str):
    tasks.append(task)
    return {"message": "Task added"}

This backend can add and read tasks.

🔹 React Example (Frontend)

import apiClient from "./apiClient";

// Create
apiClient.post("/tasks", { task: "Learn FastAPI" });

// Read
const response = await apiClient.get("/tasks");

These two lines of code connect your React app to your FastAPI backend — creating and fetching tasks seamlessly.

💡 Real-World Example: When you add a task in a to-do app, it calls the POST API. When you refresh and see all tasks again, it calls the GET API.

This simple pattern powers apps like Notion, Todoist, and ClickUp.

🔹 CRUD Pattern Summary

🔁 3. State Synchronization

🔹 The Concept

When data changes on the backend (via FastAPI), your React state should reflect those changes. Otherwise, the UI becomes outdated.

🔹 How It Works

After every CRUD operation:

1. Call the API
2. Update React state
3. Rerender the UI

Example:

const response = await apiClient.get("/tasks");
setTasks(response.data);

💡 Real-World Example: In Trello, when you add a new card, everyone else sees it instantly — that’s state synchronization.

In smaller apps, we can achieve this with periodic refreshing (polling) or by re-fetching data after updates.

🔹 Sync Strategies

🔹 Example of Polling

setInterval(async () => {
  const res = await apiClient.get("/tasks");
  setTasks(res.data);
}, 5000);

This keeps the frontend updated every 5 seconds.

⚠️ 4. Error Boundaries

🔹 The Concept

Errors can happen during API calls — for example:

• FastAPI server is down
• Invalid data sent
• Token expired

Error boundaries prevent the entire app from crashing when these occur.

🔹 Example

try {
  await apiClient.get("/tasks");
} catch (error) {
  console.error("Something went wrong:", error.message);
}

You can display a friendly message like “Server not reachable” instead of showing a blank screen.

💡 Real-World Example: When YouTube can’t load a video, it doesn’t crash — it shows a simple “Video unavailable” message. That’s an error boundary in action.

🔹 Best Practices

🧩 Summary

💡 Final Thought

React and FastAPI work perfectly together — FastAPI provides the speed and simplicity of Python APIs, while React gives users an interactive and modern interface.

When combined with smart patterns like reusable clients, clean CRUD logic, automatic state sync, and friendly error handling, you get a stable, real-world-grade application.

Apps like Trello, Asana, and Todoist use the same concepts — just on a bigger scale.