useCountdown 
useIntervalFn 的包装器,提供倒计时计时器。
演示 
用法 
ts
import { useCountdown } from '@vueuse/core'
const countdownSeconds = 5
const { remaining, start, stop, pause, resume } = useCountdown(countdownSeconds, {
  onComplete() {
  },
  onTick() {
  }
})你可以使用一个 ref 来改变初始倒计时。start() 和 resume() 也接受一个新的倒计时值用于下一次倒计时。
ts
import { useCountdown } from '@vueuse/core'
import { shallowRef } from 'vue'
const countdown = shallowRef(5)
const { start, reset } = useCountdown(countdown, {
})
// change the countdown value
countdown.value = 10
// start a new countdown with 2 seconds
start(2)
// reset the countdown to 4, but do not start it
reset(4)
// start the countdown with the current value of `countdown`
start()类型声明 
显示类型声明
ts
export interface UseCountdownOptions {
  /**
   *  Interval for the countdown in milliseconds. Default is 1000ms.
   */
  interval?: MaybeRefOrGetter<number>
  /**
   * Callback function called when the countdown reaches 0.
   */
  onComplete?: () => void
  /**
   * Callback function called on each tick of the countdown.
   */
  onTick?: () => void
  /**
   * Start the countdown immediately
   *
   * @default false
   */
  immediate?: boolean
}
export interface UseCountdownReturn extends Pausable {
  /**
   * Current countdown value.
   */
  remaining: ShallowRef<number>
  /**
   * Resets the countdown and repeatsLeft to their initial values.
   */
  reset: (countdown?: MaybeRefOrGetter<number>) => void
  /**
   * Stops the countdown and resets its state.
   */
  stop: () => void
  /**
   * Reset the countdown and start it again.
   */
  start: (countdown?: MaybeRefOrGetter<number>) => void
}
/**
 * Wrapper for `useIntervalFn` that provides a countdown timer in seconds.
 *
 * @param initialCountdown
 * @param options
 *
 * @see https://vueuse.org.cn/useCountdown
 */
export declare function useCountdown(
  initialCountdown: MaybeRefOrGetter<number>,
  options?: UseCountdownOptions,
): UseCountdownReturn