数组对象判断某个值出现的次数
例如：
let areaArr = [{areaId:1,areaName:'区域1'}，{areaId:2,areaName:'区域2'}，{areaId:1,areaName:'区域1'}]
//获取需要判断的属性
const titleList = areaArr.map(item => {
return item.areaId
})
getRepeatNum (titleList) {
return titleList.reduce((prev, next) => {
prev[next] = (prev[next] + 1) || 1
return prev
}, {})
},
console.log(this.getRepeatNum(titleList)) //{1: 2,2,1}
