refDefault

v0.0.15testeddemo

Wrap a writable `ref` so that reads fall back to a default value whenever the source holds `null` or `undefined`, while writes pass straight through to the source. The default may itself be reactive (a ref, getter, or plain value), so the fallback can track other state. Implemented as a single writable `computed` — no watchers, no extra refs, nothing to tear down — which keeps it allocation-light and SSR-safe (it never touches the DOM).

Source Tests

Examples

const raw = ref<string | null>(null);
const name = refDefault(raw, 'anonymous');
name.value; // 'anonymous'
raw.value = 'ada';
name.value; // 'ada'
name.value = 'grace';
raw.value; // 'grace' — writes pass through

// The default can be reactive
const fallback = ref('guest');
const user = refDefault(ref<string | null>(null), fallback);
fallback.value = 'visitor';
user.value; // 'visitor'

Demo

Loading demo…

Signature

export function refDefault<T>(
  source: Ref<T | null | undefined>,
  defaultValue: MaybeRefOrGetter<T>,
): RefDefaultReturn<T>{ ... }

Type Parameters

T

Parameters

Parameter	Type	Default	Description
`source`	`Ref<T \| null \| undefined, T \| null \| undefined>`	—	The source ref to read through and write back to
`defaultValue`	`MaybeRefOrGetter<T>`	—	Fallback returned when the source is `null`/`undefined` (can be reactive)

Returns

RefDefaultReturn<T>A writable computed ref that never reads as `null`/`undefined`