computed-async

Computed value backed by an async evaluator.


Package	`@vizejs/composable/computed-async`
Own the source	`vize lib pull composable:computed-async`
Runtime exports	`computedAsync`
Gzip budget	768 B

Usage

import { computedAsync } from "@vizejs/composable/computed-async";

Runtime contract

Utility	Category	Stability	SSR	Hydration	Cleanup	Targets	Host globals	Uses
`computedAsync`	reactivity	experimental	safe	stable	reactive-scope	web, server, worker, native, desktop, terminal	`AbortController`	—

API

`computedAsync`

Computed value backed by an async evaluator. Reactive dependencies read synchronously in the evaluator (before its first await) are tracked; when one changes, the previous evaluation is cancelled (its signal aborts and onCancel callbacks run) and a new one starts. Only the newest evaluation may write the result, so out-of-order responses can never win. The value holds initial until the first evaluation settles, which also keeps server and client markup identical during hydration (the server never waits for the promise). Results are stored shallowly: replace the value instead of mutating it.

function computedAsync<Value>( evaluator: (context: ComputedAsyncContext) => Value | Promise<Value>, initial: Value, options?: ComputedAsyncOptions, ): Readonly<Ref<Value>>

const user = computedAsync(
  async ({ signal }) => (await fetch(`/users/${id.value}`, { signal })).json(),
  null,
);

`computedAsync`

function computedAsync<Value>( evaluator: (context: ComputedAsyncContext) => Value | Promise<Value>, initial?: undefined, options?: ComputedAsyncOptions, ): Readonly<Ref<Value | undefined>>

`computedAsync`

function computedAsync<Value>( evaluator: (context: ComputedAsyncContext) => Value | Promise<Value>, initial?: Value, options: ComputedAsyncOptions = {}, ): Readonly<Ref<Value | undefined>>

Types

`ComputedAsyncContext`

Context handed to a computedAsync evaluator.

Member	Type	Description
`signal`	`AbortSignal`	Aborted as soon as a newer evaluation starts or the scope stops.
`onCancel`	`ComputedAsyncCancel`	Register a callback for when this evaluation becomes stale.

`ComputedAsyncOptions`

Options for computedAsync.

Member	Type	Description
`lazy`?	`boolean`	Defer the first evaluation until the value is read.
`evaluating`?	`Ref<boolean>`	Ref that is `true` while an evaluation is in flight.
`onError`?	`(error: unknown) => void`	Receives evaluator failures; the previous value is kept.