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Add comprehensive reference documentation for: - Vitest: environments, projects/workspaces, type testing, vi utilities - Pinia: HMR, Nuxt integration, SSR setup - Vue: built-in components (Transition, Teleport, Suspense, KeepAlive) and advanced directives
101 lines
1.8 KiB
Markdown
101 lines
1.8 KiB
Markdown
---
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category: Watch
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---
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# whenever
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Shorthand for watching value to be truthy.
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## Usage
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```js
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import { useAsyncState, whenever } from '@vueuse/core'
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const { state, isReady } = useAsyncState(
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fetch('https://jsonplaceholder.typicode.com/todos/1').then(t => t.json()),
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{},
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)
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whenever(isReady, () => console.log(state))
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```
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```ts
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import { whenever } from '@vueuse/core'
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// ---cut---
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// this
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whenever(ready, () => console.log(state))
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// is equivalent to:
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watch(ready, (isReady) => {
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if (isReady)
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console.log(state)
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})
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```
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### Callback Function
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Same as `watch`, the callback will be called with `cb(value, oldValue, onInvalidate)`.
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```ts
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import { whenever } from '@vueuse/core'
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// ---cut---
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whenever(height, (current, lastHeight) => {
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if (current > lastHeight)
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console.log(`Increasing height by ${current - lastHeight}`)
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})
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```
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### Computed
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Same as `watch`, you can pass a getter function to calculate on each change.
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```ts
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import { whenever } from '@vueuse/core'
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// ---cut---
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// this
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whenever(
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() => counter.value === 7,
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() => console.log('counter is 7 now!'),
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)
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```
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### Options
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Options and defaults are same with `watch`.
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```ts
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import { whenever } from '@vueuse/core'
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// ---cut---
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// this
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whenever(
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() => counter.value === 7,
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() => console.log('counter is 7 now!'),
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{ flush: 'sync' },
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)
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```
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## Type Declarations
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```ts
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export interface WheneverOptions extends WatchOptions {
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/**
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* Only trigger once when the condition is met
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*
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* Override the `once` option in `WatchOptions`
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*
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* @default false
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*/
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once?: boolean
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}
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/**
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* Shorthand for watching value to be truthy
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*
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* @see https://vueuse.org/whenever
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*/
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export declare function whenever<T>(
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source: WatchSource<T | false | null | undefined>,
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cb: WatchCallback<T>,
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options?: WheneverOptions,
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): WatchHandle
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```
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