Raising Exceptions in JavaScript
To throw an exception from an operation implementation, you simply instantiate the exception, initialize it, and throw it. For example:
// ...
write: function(text, current) {
try {
// Try to write file contents here...
}
catch(err) {
var ex = new GenericError("Exception during write operation");
ex.ice_cause = err; // Not returned to client but may be useful
throw ex;
}
}
If you throw an arbitrary JavaScript error (such as an instance of Error), the Ice run time catches the exception and then returns an UnknownException to the client. Similarly, if you throw an "impossible" user exception (a user exception that is not listed in the exception specification of the operation), the client receives an UnknownUserException.
If you throw an Ice run-time exception, such as MemoryLimitException, the client receives an UnknownLocalException. For that reason, you should never throw system exceptions from operation implementations. If you do, all the client will see is an UnknownLocalException, which does not tell the client anything useful.
Three run-time exceptions are treated specially and not changed to UnknownLocalException when returned to the client: ObjectNotExistException, OperationNotExistException, and FacetNotExistException.