---
title: Callbacks
description: Run your own code in a SvelteKit app when a visitor records a
  choice or permissions change, with onChoiceRecorded, onPermissionsChanged and
  script callbacks.
group: frameworks
lastModified: "2026-10-10T16:01:45+01:00"
---
## Pick the right callback

Run your own code when consent changes through the provider's `callbacks`
prop, a script's own callbacks, or a kernel event in one component:

|You want to|Use|
|--|--|
|Send a choice to your analytics or CRM when the visitor makes one|`callbacks.onChoiceRecorded`|
|Start or stop your own code when what may run changes|`callbacks.onPermissionsChanged`|
|Report failed backend requests|`callbacks.onError`|
|Show a message or flush data before a withdrawal reloads the page|`callbacks.onBeforeConsentRevocationReload`|
|Call a vendor's own consent API after its script loads|The script's `onConsentChange`|
|React to consent inside one component|`getConsentKernel().events.on()` or the manager's properties|

## onChoiceRecorded or onPermissionsChanged

`onChoiceRecorded` runs only when the visitor accepts, rejects or saves.
`onPermissionsChanged` runs whenever effective permissions change, whatever
the cause:

|Event|`onChoiceRecorded`|`onPermissionsChanged`|
|--|--|--|
|Visitor accepts, rejects or saves|Yes|Yes, if a permission changed|
|Policy resolves under opt-out and allows categories before a choice|No|Yes|
|Global Privacy Control overrides a grant|No|Yes|
|A recorded choice expires|No|Yes|
|Visitor dismisses a notice|No|No|

Use `onChoiceRecorded` for consent records and audit trails, because it fires
only for a visitor's action. Use `onPermissionsChanged` to start or stop code,
because it covers every way a permission changes. Never treat
`onPermissionsChanged` as proof that the visitor agreed to something.

## Pass callbacks to the provider

```ts title="src/lib/consent-callbacks.ts"
import type { ConsentProviderCallbacks } from '@c15t/svelte';

// Pass as `callbacks={callbacks}` on ConsentProvider.
export const callbacks: ConsentProviderCallbacks = {
	// Runs just before c15t reloads the page after a withdrawal.
	onBeforeConsentRevocationReload: ({ preferences }) => {
		console.info('Reloading with', preferences);
	},
	// An explicit accept, reject or save. Never runs for defaults, expiry,
	// policy changes or privacy signals.
	onChoiceRecorded: ({ snapshot, confirmed }) => {
		console.info('Visitor chose', snapshot.explicitChoice, confirmed);
	},
	// A failed command, such as an /init request that could not reach the
	// backend.
	onError: ({ error }) => {
		console.warn('c15t error', error);
	},
	// Any change to what may run, whatever caused it.
	onPermissionsChanged: ({ snapshot, previous }) => {
		console.info('Permissions', previous, '->', snapshot.effectivePermissions);
	},
};
```

Pass the object as `callbacks={callbacks}` on `ConsentProvider`. The
provider reads it once, when it is created. Keep the functions in a module or
in the component that renders the provider; on SvelteKit, not in a server
load, because a load cannot send functions to the browser.

|Callback|Payload|
|--|--|
|`onChoiceRecorded`|`snapshot`, the state after the choice; `confirmed`, the categories this action recorded; `actionAt`, the time.|
|`onPermissionsChanged`|`snapshot`, the state after the change; `previous`, the permissions before it.|
|`onError`|`error`, a message string.|
|`onBeforeConsentRevocationReload`|`preferences`, the permissions after the withdrawal.|

Callbacks run after c15t updates its own state, so `snapshot` and
`getConsentManager()` already hold the new values. Visitor actions happen in
the browser, so in practice that is where the callbacks run.

`onBeforeConsentRevocationReload` runs synchronously right before the reload.
Keep it short; the page is about to unload. It does not run when you set
`reloadOnConsentRevoked={false}`.

## Script callbacks

Each entry in `scripts` takes its own callbacks:

|Callback|Runs|
|--|--|
|`onBeforeLoad`|Before the loader adds the script.|
|`onLoad`|When the script loaded.|
|`onError`|When the script failed to load.|
|`onConsentChange`|When consent changes after the script loaded. Use it to call the vendor's own consent API.|
|`onDispose`|When the configuration is removed or the provider unmounts.|

Helpers from `@c15t/integrations` already set these for their vendor.
[Building integrations](/docs/integrations/building-integrations) shows how to
write them.

## Listen inside one component

For a component that shows or reacts to consent, subscribe to a kernel event
in `$effect`, so the listener goes away with the component. The
[context getters](./getters#listen-to-consent-events) page has the example.
For values you render, read the manager's properties instead; they update the
component without a listener.

## Verify the callbacks

Open the console, clear site data and reload:

1. Accept in the banner. `onChoiceRecorded` and `onPermissionsChanged` both
   log.
2. Dismiss a notice, if your policy shows one. Neither logs.
3. Withdraw a category you allowed. `onBeforeConsentRevocationReload` logs,
   then the page reloads.