computedAsync

类别

响应性

导出大小

347 B

最后更改

3 周前

别名

asyncComputed

用于异步函数的计算属性

用法

import { computedAsync } from '@vueuse/core'
import { shallowRef } from 'vue'

const name = shallowRef('jack')

const userInfo = computedAsync(
  async () => {
    return await mockLookUp(name.value)
  },
  null, // initial state
)

评估状态

您需要传递一个 ref 来跟踪异步函数是否正在评估。

import { computedAsync } from '@vueuse/core'
import { shallowRef } from 'vue'

const evaluating = shallowRef(false)

const userInfo = computedAsync(
  async () => { /* your logic */ },
  null,
  evaluating,
)

onCancel

当计算源在先前的异步函数解析之前发生更改时，您可能需要取消先前的异步函数。这是一个展示如何与 fetch API 结合使用的示例。

const packageName = shallowRef('@vueuse/core')

const downloads = computedAsync(async (onCancel) => {
  const abortController = new AbortController()

  onCancel(() => abortController.abort())

  return await fetch(
    `https://api.npmjs.org/downloads/point/last-week/${packageName.value}`,
    { signal: abortController.signal },
  )
    .then(response => response.ok ? response.json() : { downloads: '—' })
    .then(result => result.downloads)
}, 0)

懒加载

默认情况下，computedAsync 将在创建时立即开始解析，指定 lazy: true 使其在首次访问时开始解析。

import { computedAsync } from '@vueuse/core'
import { shallowRef } from 'vue'

const evaluating = shallowRef(false)

const userInfo = computedAsync(
  async () => { /* your logic */ },
  null,
  { lazy: true, evaluating },
)

注意事项

就像 Vue 的内置 computed 函数一样，computedAsync 执行依赖跟踪，并在依赖项更改时自动重新评估。但请注意，只有首次调用堆栈中引用的依赖项才会被考虑。换句话说：异步访问的依赖项不会触发异步计算值的重新评估。
与 Vue 的内置 computed 函数相反，每当依赖项发生更改时，无论其结果当前是否正在被跟踪，都会触发异步计算值的重新评估。

类型声明

显示类型声明

typescript

/**
 * Handle overlapping async evaluations.
 *
 * @param cancelCallback The provided callback is invoked when a re-evaluation of the computed value is triggered before the previous one finished
 */
export type AsyncComputedOnCancel = (cancelCallback: Fn) => void
export interface AsyncComputedOptions {
  /**
   * Should value be evaluated lazily
   *
   * @default false
   */
  lazy?: boolean
  /**
   * Ref passed to receive the updated of async evaluation
   */
  evaluating?: Ref<boolean>
  /**
   * Use shallowRef
   *
   * @default true
   */
  shallow?: boolean
  /**
   * Callback when error is caught.
   */
  onError?: (e: unknown) => void
}
/**
 * Create an asynchronous computed dependency.
 *
 * @see https://vueuse.org.cn/computedAsync
 * @param evaluationCallback     The promise-returning callback which generates the computed value
 * @param initialState           The initial state, used until the first evaluation finishes
 * @param optionsOrRef           Additional options or a ref passed to receive the updates of the async evaluation
 */
export declare function computedAsync<T>(
  evaluationCallback: (onCancel: AsyncComputedOnCancel) => T | Promise<T>,
  initialState: T,
  optionsOrRef?: Ref<boolean> | AsyncComputedOptions,
): Ref<T>
export declare function computedAsync<T>(
  evaluationCallback: (onCancel: AsyncComputedOnCancel) => T | Promise<T>,
  initialState?: undefined,
  optionsOrRef?: Ref<boolean> | AsyncComputedOptions,
): Ref<T | undefined>
export { computedAsync as asyncComputed }