AfterUpdate

AfterUpdate is a term used for a lifecycle hook in several component frameworks that runs code after a component has been updated and the DOM has been refreshed. It is typically used to perform operations that rely on the latest DOM state or on new data resulting from recent updates.

In Svelte, afterUpdate is a specific API you can use to register a callback that executes after every update cycle. It is imported from the framework and invoked with a function, for example: afterUpdate(() => { /* post-update logic here */ }). The callback runs after the DOM has been updated following any reactive state change. It does not replace onMount, which runs only after the initial render; afterUpdate handles subsequent updates. Use it for DOM measurements, interfacing with non-Svelte libraries, or triggering animations that should occur after the latest changes.

Practical considerations include avoiding infinite loops: if code inside afterUpdate mutates state in a way that triggers another update, it can cause repeated executions. To prevent this, guard the logic with conditions or flags that ensure the code runs only as intended. Cleanup considerations are typically handled with separate lifecycle hooks (for example, onDestroy) when resources registered in afterUpdate need disposal.

While afterUpdate is commonly associated with Svelte, other frameworks offer analogous hooks—such as updated in Vue or componentDidUpdate equivalents in React—each serving a similar purpose: running code after a component has completed rendering updates, but with framework-specific semantics and lifecycle management.