simple-sandbox-app#

Minimal repro app to prove that Server-Sent Events (SSE) work over a public Vercel Sandbox port.

What this does#

• Serves an HTML page on /.
• Opens an EventSource connection from the browser to /events.
• Streams timestamps every 500ms from the server using SSE framing (data: ...\n\n).
• Runs the same app inside a public sandbox and prints a public URL.

Files#

• index.ts - Bun server with two routes:
  • / serves index.html
  • /events streams SSE with appropriate headers
• index.html - Vanilla JS client that connects with EventSource and renders incoming events
• run-on-sandbox.ts - Creates a Vercel Sandbox, uploads app files, starts Bun, and prints the public URL

Local run#

Install dependencies:

bun install

Start the app locally:

bun run index.ts

Then open:

http://localhost:8081/

Optional stream check from terminal:

curl -N http://localhost:8081/events

Run in Vercel Sandbox (public port repro)#

bun run run-on-sandbox.ts

The script prints a public URL for port 8081. Open that URL and verify:

• The page status becomes connected
• New timestamp events keep appearing

This is the repro target: SSE remains functional when exposed via a public Sandbox port.