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onError

Runs cleanup after the source reports a failure cause.

Package version
2.0.0-beta.13
Category
Observing failures
Since
1.0.0

Follow one execution

Runs cleanup after the source reports a failure cause.

Fx timelineonError forwards the original failure before starting failure-only cleanuponError
OperatoronError(logCause)
Read this diagram

Follow each lane from left to right. Events stacked vertically share a tick; the green cursor marks the current time across every lane.

  • A value
    The text inside the pill is the emitted value.
  • Work starts
    The raised chevron starts an inner run (^ in the source).
  • The run returns
    The vertical bar ends this lane’s run.
  • A cause is delivered
    The exclamation mark belongs to this lane.
  • Work is interrupted
    The cross marks cancellation of this run.
  • Current time
    The line and diamond move together across all lanes.
  • Happening now
    A highlighted event is at the current tick.
  • Still ahead
    Muted, dashed values have not happened yet.
  • Time continues
    The lane’s arrow is not a return marker. An empty stretch can be quiet work that is still running.

Illustrated ticks start at 0. At 1×, one illustrated tick takes one second; captions specify real durations when timing matters. A cause or interruption belongs to its lane, and other work may continue. Scroll horizontally to inspect the rest of a long timeline.

The original cause is delivered downstream first. Cleanup runs only if that downstream onFailure Effect succeeds; if the sink itself fails or interrupts, flatMap never reaches cleanup. Typed cleanup failure is impossible by signature, but Effect.ignore does not suppress defects or interruption: either can fail or interrupt the run after the source Cause was handled. Its services are required for the subscription, and it does not run after success.

Source implementation · Learn the surrounding model

Compare all Fx timelines →

Import

import { onError } from "@typed/fx/Fx";

Signatures

export declare const onError: {
    <E, X, R2>(cleanup: (cause: Cause.Cause<E>) => Effect.Effect<X, never, R2>): <A, R>(self: Fx<A, E, R>) => Fx<A, E, R | R2>;
    <A, E, R, X, R2>(self: Fx<A, E, R>, cleanup: (cause: Cause.Cause<E>) => Effect.Effect<X, never, R2>): Fx<A, E, R | R2>;
};

Why

Failure-only observation belongs at the stream boundary when cleanup needs the complete Cause rather than merely the typed error.

Ownership and lifetime

The original cause is delivered downstream first. Cleanup runs only if that downstream onFailure Effect succeeds; if the sink itself fails or interrupts, flatMap never reaches cleanup. Typed cleanup failure is impossible by signature, but Effect.ignore does not suppress defects or interruption: either can fail or interrupt the run after the source Cause was handled. Its services are required for the subscription, and it does not run after success.

Examples

import { Effect } from "effect"
import { onError } from "@typed/fx/Fx"
import { fail } from "@typed/fx/Fx"

const logged = onError(fail("offline"), (cause) => Effect.logError(cause))
A cleanup defect is not a typed failure
```ts
import { Effect } from "effect"
import { onError } from "@typed/fx/Fx"
import { fail } from "@typed/fx/Fx"

const defectiveCleanup = onError(fail("offline"), () => Effect.die("logger defect"))
```

Other public imports

These import paths expose the same declaration. Each page retains its own public name and signature.

Source