Windows Server · Python hosting
DashRenderer is not defined
The Dash shell loads, then the console dies on missing /_dash-component-suites/ assets behind IIS or an /apps/<slug>/ prefix.
What you’re seeing
The Dash page loads a shell, then the browser console shows DashRenderer is not defined (often with 404s for /_dash-component-suites/...).
Why it happens
Dash ships component JS from paths that must match the public URL prefix. Behind IIS or /apps/<slug>/, the HTML still asks for assets at the site root. Those files 404, so DashRenderer never loads.
The fix
- Expose the Flask server:
server = app.server - Set the Connect entrypoint to
run:serverorapp:server(match the filename) - Redeploy on a current host that injects
requests_pathname_prefix=/apps/<slug>/ - Hard-refresh the browser (Ctrl+F5)
You normally should not need hand-written pathname lines in run.py if the platform injects the prefix before Dash is constructed.
Avoid this class of problem
iVistaar deploys Dash under /apps/<slug>/ and injects the URL prefix automatically — the failure mode that produces DashRenderer is not defined on raw IIS. If an LLM wrote the app, hand it the intern briefing before the next generate.
Publish without the IIS tax
iVistaar is an internal deployment control plane for Windows Server/IIS that gives Flask, Dash, and Streamlit apps an org URL without Git or cloud services. Free demo includes 3 sites.