I've been asked to add a "failover" in our JS apps in case we lose access to the public internet or Esri's CDN goes offline. So we're hosting a copy of the API locally, but we don't have the infrastructure to speedily deliver it to our geographically dispersed customers. What I was thinking was to run a quick check on app load that tests access to Esri's CDN, and only point to our locally hosted version if that request fails.
Is there a JS API "health check" endpoint so to speak? If not that, what is the smallest possible resource I could test from js.arcgis.com to ensure connectivity?