|Expanded Error Panel (Summer ’17)||Error Panel With Limited Details (prior releases)|
The error panel appears only when a relevant error occurs in Lightning Experience or Salesforce1. The expandable stack trace appears only on desktop and tablet form factors—not on a phone.
The improved error reporting affects only your custom components, not standard components provided with the framework. Outside of Lightning Experience and Salesforce1, for example, in Lightning Out or a standalone app, error output can include details that were previously omitted, such as a complete stack trace.