uniapp小程序，实现每次进入页面时自动开启 30 秒的倒计时。

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<view class="number">{{count}}</view> <!-- 倒计时数字 --> data() {     return {       count: 30,       timer: null,     }; }, methods: {       countDown() {         let _this = this;         const TIME_COUNT = 30;         if (!this.timer) {             this.count = TIME_COUNT;             this.timer = setInterval(() => {         if (this.count > 0 && this.count <= TIME_COUNT) {             this.count--;         } else {             clearInterval(this.timer);             this.timer = null;           }         }, 1000);       }     }, }, onShow() {     this.countDown(); }