Why is my React frontend not displaying POST data from my FastAPI backend?

React not displaying POST response from FastAPI backend: Troubleshooting CORS

In this issue, a React frontend is unable to display data POSTed from a FastAPI backend. The issue lies in CORS (Cross-Origin Resource Sharing) restrictions, which need to be configured on the FastAPI backend.

CORS and FastAPI

CORS is a mechanism that restricts cross-origin requests, such as those from a React frontend to a FastAPI backend. This is done to mitigate security risks and protect user data. To enable CORS, you need to configure the FastAPI application to allow requests from the frontend origin.

Configuring CORS in FastAPI

One of the recommended ways to enable CORS in FastAPI is through the CORSMiddleware. Here's an example:

from fastapi import FastAPI
from fastapi.middleware.cors import CORSMiddleware

app = FastAPI()

origins = ["http://localhost:3000", "http://127.0.0.1:3000"]

app.add_middleware(
    CORSMiddleware,
    allow_origins=origins,
    allow_credentials=True,
    allow_methods=["*"],
    allow_headers=["*"],
)

By adding this middleware, you are allowing requests from the specified origins (in this case, localhost:3000) and providing permissions for cookies, methods, and headers.

Resolving the issue

To resolve the issue, ensure that the FastAPI backend has CORS configured as shown above. Once CORS is enabled, the React frontend should be able to communicate with the backend and display the data received from the POST request.

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