判断数组里的元素出现的次数以及元素

 //判断数组里元素出现的次数
    getShowAcount(names) {
      var countedNames = names.reduce((obj, name) => {
        if (name in obj) {
          obj[name]++
        } else {
          obj[name] = 1
        }
        return obj
      }, {})
      //reduce的第二个参数就是obj的初始值
      return countedNames
    },
    let names = ['a','b','c','a']
    let obj= this.getShowAcount(names) //{a:2}