Updating Item List in Jinja2 Template Using FastAPI WebSockets

In a comment system, maintaining an up-to-date list of comments is crucial for delivering a seamless user experience. When a new comment is added, it should be reflected in the template without the need for manual reloading.

In Jinja2, updating the comment list is typically achieved through API calls. However, this approach can introduce latency and compromise the user interface's responsiveness. A more efficient solution involves leveraging real-time communication technologies like WebSockets.

Implementing WebSockets in FastAPI and Jinja2

WebSockets, a subset of the WebSocket Protocol, provide a two-way communication channel between a client (browser) and a server (backend). This allows us to broadcast real-time updates to clients, including newly added comments.

To implement WebSockets in this scenario, we'll utilize FastAPI and its built-in WebSocket functionality. The code snippet below demonstrates how to create a WebSocket endpoint:

from fastapi import FastAPI, WebSocket, WebSocketDisconnect

app = FastAPI()

@app.websocket("/ws")
async def websocket_endpoint(websocket: WebSocket):
    # WebSocket handling
    ...

Within the websocket_endpoint function, we establish a WebSocket connection with the client and handle incoming data. When a new comment is received, we'll broadcast it to all connected clients using the broadcast() method.

Updating the Jinja2 Template

To update the Jinja2 template with the new comment, we use the onmessage event listener in the front-end JavaScript. When a new comment message is received, we create a new