stack/v1/packages/mosaic/framework/skills/vueuse-functions/references/whenever.md

category

category
Watch

whenever

Shorthand for watching value to be truthy.

Usage

import { useAsyncState, whenever } from '@vueuse/core';

const { state, isReady } = useAsyncState(
  fetch('https://jsonplaceholder.typicode.com/todos/1').then((t) => t.json()),
  {},
);

whenever(isReady, () => console.log(state));

import { whenever } from '@vueuse/core';
// ---cut---
// this
whenever(ready, () => console.log(state));

// is equivalent to:
watch(ready, (isReady) => {
  if (isReady) console.log(state);
});

Callback Function

Same as watch, the callback will be called with cb(value, oldValue, onInvalidate).

import { whenever } from '@vueuse/core';
// ---cut---
whenever(height, (current, lastHeight) => {
  if (current > lastHeight) console.log(`Increasing height by ${current - lastHeight}`);
});

Computed

Same as watch, you can pass a getter function to calculate on each change.

import { whenever } from '@vueuse/core';
// ---cut---
// this
whenever(
  () => counter.value === 7,
  () => console.log('counter is 7 now!'),
);

Options

Options and defaults are same with watch.

import { whenever } from '@vueuse/core';
// ---cut---
// this
whenever(
  () => counter.value === 7,
  () => console.log('counter is 7 now!'),
  { flush: 'sync' },
);

Type Declarations

export interface WheneverOptions extends WatchOptions {
  /**
   * Only trigger once when the condition is met
   *
   * Override the `once` option in `WatchOptions`
   *
   * @default false
   */
  once?: boolean;
}
/**
 * Shorthand for watching value to be truthy
 *
 * @see https://vueuse.org/whenever
 */
export declare function whenever<T>(
  source: WatchSource<T | false | null | undefined>,
  cb: WatchCallback<T>,
  options?: WheneverOptions,
): WatchHandle;