FastAPI + Frontend Interaction: Practical JavaScript Call to FastAPI API

This article introduces the interaction methods between a FastAPI backend and frontend JavaScript. The core principle is that the frontend calls the backend API through HTTP requests, and the backend returns JSON data after processing, which the frontend then renders and displays. Prerequisites: The backend needs to install FastAPI and uvicorn, while the frontend only requires HTML + JS. The backend writes main.py to implement three interfaces: GET (/api/hello) returns a message, GET (/api/items/{item_id}) with parameters returns product information, and POST (/api/submit) receives data and provides feedback. CORSMiddleware is configured to handle cross-origin issues (allowing all origins during development and specifying domains in production). On the frontend, the fetch API is used to call the interfaces. Three buttons respectively trigger the requests, parse the JSON, and display the results. During runtime, start the backend service and open the frontend page to test. Key knowledge points include cross-origin configuration, HTTP methods (GET/POST), JSON data exchange, and error handling. For advanced exploration, one can look into Axios, frontend frameworks, and data validation.