为什么我从 getters 得到的错误数组不是函数 Vuex？

Question

在用到达点和出发点填充输入并用选择过滤航班后，我收到错误 this.flights.filter is not a function，即使航班来自 getters 并且是一种数组。我错过了什么吗？

https://stackblitz.com/edit/vue-hrqfyc?file=src%2Fcomponents%2FSearchBtn.vue,src%2Fcomponents%2FFilters.vue,src%2Fstore%2Findex.js,src%2FApp.vue,src% 2Fcomponents%2FFlight.vue,src%2Fcomponents%2FFlightList.vue,src%2Fcomponents%2FArrivalPoint.vue,src%2Fcomponents%2FDeparturePoint.vue

computed: {
    flights() {
      return this.$store.getters.getFlights;
    },
    // filtered computed flights for selectors
    flightsClasses() {
      return this.flights.filter((item, index, objects) => {
        if (index === 0) {
          return item;
        } else if (item.trip_class !== objects[index - 1].trip_class) {
          return item;
        }
      }).sort(function(a, b){return a-b});
    },
  }
}