When you click on an error message from the JavaScript Error Dashboard, you are directed to the Summary tab which displays the following metrics:

• Impacted Pageviews: Number of Pageviews (instances of browser app web pages) impacted by the error
• Error instances: Number of error instances across all web pages
• % of total error instances: One specific error divided by the total number of errors (across all web pages)
• Errors per minute: How many times this specific error occurred per minute
• First occurrence: Timestamp of the first error occurrence