where is comfyui server host and port defined?

[CharlesJu1]

On startup, the ComfyUI_frontend will connect to ComfyUI backend at 127.0.0.1:8188. If the ComfyUI backend server is not up, it gives an error.

1:11:47 AM [vite] http proxy error: /api/users
Error: connect ECONNREFUSED 127.0.0.1:8188
    at TCPConnectWrap.afterConnect [as oncomplete] (node:net:1610:16)
    at TCPConnectWrap.callbackTrampoline (node:internal/async_hooks:130:17)

However, I could not find where in ComfyUI_frontend the backend server URL 127.0.0.1:8188 is defined. Could someone point out?