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feat(watchOnce): use vue's native once behaviour #4750

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Merged
merged 1 commit into from
May 14, 2025
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feat(watchOnce): use vue's native once behaviour #4750

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11 changes: 3 additions & 8 deletions packages/shared/watchOnce/index.md
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Original file line number Diff line number Diff line change
Expand Up @@ -4,17 +4,12 @@ category: Watch

# watchOnce

`watch` that only triggers once.

::: tip

[Once Watcher](https://vuejs.org/guide/essentials/watchers.html#once-watchers) has been added to Vue [since 3.4](https://github.com/vuejs/core/pull/9034), use `watch(watchSource, callback, { once: true })` instead on supported versions.

:::
Shorthand for watching value with `{ once: true }`. Once the callback fires once, the watcher will be stopped.
See [Vue's docs](https://vuejs.org/guide/essentials/watchers.html#once-watchers) for full details.

## Usage

After the callback function has been triggered once, the watch will be stopped automatically.
Similar to `watch`, but with `{ once: true }`

```ts
import { watchOnce } from '@vueuse/core'
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45 changes: 30 additions & 15 deletions packages/shared/watchOnce/index.ts
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Original file line number Diff line number Diff line change
@@ -1,23 +1,38 @@
import type { WatchCallback, WatchOptions, WatchSource, WatchStopHandle } from 'vue'
import type { MapOldSources, MapSources } from '../utils'
import { nextTick, watch } from 'vue'
import { watch } from 'vue'

// overloads
export function watchOnce<T extends Readonly<WatchSource<unknown>[]>, Immediate extends Readonly<boolean> = false>(source: [...T], cb: WatchCallback<MapSources<T>, MapOldSources<T, Immediate>>, options?: WatchOptions<Immediate>): WatchStopHandle
export function watchOnce<T extends Readonly<WatchSource<unknown>[]>>(
source: [...T],
cb: WatchCallback<MapSources<T>, MapOldSources<T, true>>,
options?: Omit<WatchOptions<true>, 'once'>
): WatchStopHandle

export function watchOnce<T, Immediate extends Readonly<boolean> = false>(sources: WatchSource<T>, cb: WatchCallback<T, Immediate extends true ? T | undefined : T>, options?: WatchOptions<Immediate>): WatchStopHandle
export function watchOnce<T>(
source: WatchSource<T>,
cb: WatchCallback<T, T | undefined>,
options?: Omit<WatchOptions<true>, 'once'>
): WatchStopHandle

// implementation
export function watchOnce<Immediate extends Readonly<boolean> = false>(
source: any,
cb: any,
options?: WatchOptions<Immediate>,
): WatchStopHandle {
const stop = watch(source, (...args) => {
nextTick(() => stop())
export function watchOnce<T extends object>(
source: T,
cb: WatchCallback<T, T | undefined>,
options?: Omit<WatchOptions<true>, 'once'>
): WatchStopHandle

return cb(...args)
}, options)

return stop
/**
* Shorthand for watching value with { once: true }
*
* @see https://vueuse.org/watchOnce
*/
export function watchOnce<T = any>(source: T, cb: any, options?: Omit<WatchOptions, 'once'>) {
return watch(
source as any,
cb,
{
...options,
once: true,
},
)
}
Comment on lines +29 to 38
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Suggested change
export function watchOnce<T = any>(source: T, cb: any, options?: Omit<WatchOptions, 'once'>) {
return watch(
source as any,
cb,
{
...options,
once: true,
},
)
}
export function watchOnce<T = any, Immediate extends Readonly<boolean> = false>(source: T | WatchSource<T>, cb: any, options?: Omit<WatchOptions<Immediate>, 'once'>) {
return watch(
source,
cb,
{
...options,
once: true,
},
)
}

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@OrbisK Why? To keep compat?

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yeah, and to be as close as possible to native watch

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not sure if we need to, but maybe we want to overload like vue does:

https://github.com/vuejs/core/blob/1f98a9c493d01c21befa90107f0593bc92a58932/packages/runtime-core/src/apiWatch.ts#L87-L140

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@OrbisK Shall we do the same with the other watch shortcuts I guess.

I wonder as well why we don't do rest parameters and typeof watch (with a tail-like helper like the ones in type-fest to overwrite just the last parameter) so we don't have to keep this up to date ever...

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we can do, but does this work with the generics and overloads?