docs(@vant/use): add useCountDown document

packages/vant-use/.vuepress/config.js

@@ -21,7 +21,7 @@ module.exports = {
       {
         title: 'State',
         collapsable: false,
-        children: ['/src/useToggle/'],
+        children: ['/src/useToggle/', '/src/useCountDown/'],
       },
       {
         title: 'DOM',

packages/vant-use/src/useCountDown/README.md

@@ -0,0 +1,118 @@
+# useCountDown
+
+提供倒计时管理能力。
+
+## 代码演示
+
+### 基本用法
+
+```html
+<span>总时间：{{ current.total }}</span>
+<span>剩余天数：{{ current.days }}</span>
+<span>剩余小时：{{ current.hours }}</span>
+<span>剩余分钟：{{ current.minutes }}</span>
+<span>剩余秒数：{{ current.seconds }}</span>
+<span>剩余毫秒：{{ current.milliseconds }}</span>
+```
+
+```js
+import { useCountDown } from '@vant/use';
+
+export default {
+  setup() {
+    const countDown = useCountDown({
+      // 倒计时 24 小时
+      time: 24 * 60 * 60 * 1000,
+    });
+
+    // 开始倒计时
+    countDown.start();
+
+    return {
+      current: countDown.current,
+    };
+  },
+};
+```
+
+### 毫秒级渲染
+
+倒计时默认每秒渲染一次，设置 millisecond 属性可以开启毫秒级渲染。
+
+```js
+import { useCountDown } from '@vant/use';
+
+export default {
+  setup() {
+    const countDown = useCountDown({
+      time: 24 * 60 * 60 * 1000,
+      millisecond: true,
+    });
+    countDown.start();
+
+    return {
+      current: countDown.current,
+    };
+  },
+};
+```
+
+## API
+
+### 类型定义
+
+```ts
+function useCountDown(options: UseCountDownOptions): CountDown;
+
+type UseCountDownOptions = {
+  time: number;
+  millisecond?: boolean;
+  onChange?: (current: CurrentTime) => void;
+  onFinish?: () => void;
+};
+
+type CountDown = {
+  start: () => void;
+  pause: () => void;
+  reset: (totalTime: number) => void;
+  current: ComputedRef<CurrentTime>;
+};
+
+type CurrentTime = {
+  days: number;
+  hours: number;
+  total: number;
+  minutes: number;
+  seconds: number;
+  milliseconds: number;
+};
+```
+
+### 参数
+
+| 参数 | 说明 | 类型 | 默认值 |
+| --- | --- | --- | --- |
+| time | 倒计时时长，单位毫秒 | _number_ | - |
+| millisecond | 是否开启毫秒级渲染 | _boolean_ | `false` |
+| onChange | 倒计时改变时触发的回调函数 | _(current: CurrentTime) => void_ | - |
+| onFinish | 倒计时结束时触发的回调函数 | - |
+
+### 返回值
+
+| 参数    | 说明                               | 类型                    |
+| ------- | ---------------------------------- | ----------------------- |
+| current | 当前剩余的时间                     | _CurrentTime_           |
+| start   | 开始倒计时                         | _() => void_            |
+| pause   | 暂停倒计时                         | _() => void_            |
+| reset   | 重置倒计时，支持传入新的倒计时时长 | _(time?: number): void_ |
+
+### CurrentTime 格式
+
+| 名称         | 说明                   | 类型     |
+| ------------ | ---------------------- | -------- |
+| total        | 剩余总时间（单位毫秒） | _number_ |
+| days         | 剩余天数               | _number_ |
+| hours        | 剩余小时               | _number_ |
+| minutes      | 剩余分钟               | _number_ |
+| seconds      | 剩余秒数               | _number_ |
+| milliseconds | 剩余毫秒               | _number_ |