Adds an event handler that runs when an error occurs.
The onError()
function allows you to perform actions after a dataset
operation causes an error such as a field failing validation.
The value of the handler's operation
property is the
name of the function that caused the error.
For example, the operation
property could be any of the following:
"new"
"next"
"save"
"previous"
handler(operation: string, error: DatasetError): void The error handler.