例如：同一个集合中随机A类型10条，B类型取20条，C类型取10条

求解答

wxml: <view class='tip'>计时器{{h}}:{{m}}:{{s}}</view>  <button class='but bg-blue on'   bindtap="taskStart">任务开始</button>  <button class='but bg-blue on' bindtap="taskEnd">任务结束</button> js: Page({   data:{     h:'00',     m:'00',     s:'00',  //存储计时器   setInter:'',   num:1, },    /**    * 生命周期函数--监听页面加载    */   onLoad: function (options) {   // this.queryTime()   }, // 计时器 queryTime(){  const that=this;  var hou=that.data.h  var min=that.data.m  var sec=that.data.s  that.data.setInter  = setInterval(function(){      sec++      if(sec>=60){       sec=0       min++       if(min>=60){         min=0         hou++         that.setData({           h:(hou<10?'0'+min:min)         })       }else{         that.setData({           m:(min<10?'0'+min:min)         })       }      }else{        that.setData({          s:(sec<10?'0'+sec:sec)        })      }          var numVal = that.data.num + 1;        that.setData({ num: numVal });        console.log('setInterval==' + that.data.num);    },1000) },  taskStart(){    this.queryTime()  },  taskEnd(){    //清除计时器  即清除setInter    clearInterval(that.data.setInter)  },  onUnload: function () {    var that =this;    //清除计时器  即清除setInter    clearInterval(that.data.setInter) }, })