onErrorerror

onErrorerror is a term used in software engineering to describe a situation in which the process of handling an error itself triggers new errors, creating a cascade that obscures the original problem. The term is not tied to a specific language or library, but arises in discussion of asynchronous and event-driven code, where error handlers execute in separate contexts and may fail, rethrow, or rely on resources that can fail.

Origins and meaning: It is used to emphasize the risk that error-handling paths can produce secondary failures, making debugging harder. In promise chains or reactive streams, a catch or onError callback may throw or reject, producing a second error that appears to be the root cause when it is a consequence of the first.

Common causes: throwing exceptions from within an error handler, unhandled rejections inside a catch block, logging or I/O operations that fail, or cleanup code that crashes. Consequences include obscured root cause, duplicate log entries, and unstable behavior.

Mitigation: design error handling to be resilient; avoid performing nonessential operations in error paths; implement dedicated fallback strategies or error boundaries; in UI frameworks, use error boundaries or centralized error handlers; ensure that error handlers do not assume success of operations outside their scope; capture and report both original and secondary errors, preserve the original stack trace when rethrowing, and avoid silent failures.

Relation to related concepts: it is closely related to error cascades, fail-fast design, and robust debugging practices. See also: error handling, exception management, error boundary, catchError in reactive programming.