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.
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.