message property
a human-readable string which provides specific diagnostic information to help the reader understand the error condition which occurred; specifically, it isn't simply a summary of what the error code means, but actual diagnostic information to help in understanding what exactly went wrong. This text and its format is not defined by the specification and will vary from one user agent to another. If no diagnostics are available, or no explanation can be provided, this value is an empty string ("").
Implementation
final String message;