空境界

連動式下選單，分三部份

1. templeate

2. 資料結構

3. function

不使用套件

<template>
 <div>

  <b-form-select
      label="Country"
      v-model="reportFilterData.country"
      :options="showCountries()"
  ></b-form-select>

  <b-form-select
      v-if="reportFilterData.country"
      label="City"
      v-model="reportFilterData.city"
      :options="showCities()"
  ></b-form-select>

  <b-form-select
      v-if="reportFilterData.city"
      label="Region"
      v-model="reportFilterData.region"
      :options="showRegions()"
  ></b-form-select>

  <b-form-select
      v-if="reportFilterData.region"
      label="Site"
      v-model="reportFilterData.site"
      :options="showSites()"
  ></b-form-select>

  <b-form-select
      :label="Floor"
      v-model="reportFilterData.floor"
      :options="showFloors()"
  ></b-form-select>
 </div>
</template>

// selectItem
private Areas: any = [
    {
        id: "taiwan",
        text: "Taiwan",
        sub: [
            {
                id: "taipei",
                text: "Taipei",
                sub: [
                    {
                        id: "daan",
                        text: "Daan",
                        sub: [
                            {
                                id: "daan1",
                                text: "Daan1",
                                sub: [
                                    { id: "daan1_1f", text: "1F" },
                                    { id: "daan1_2f", text: "2F" },
                                    { id: "daan1_2f", text: "3F" }
                                ]
                            },
                            {
                                id: "daan2",
                                text: "Daan2",
                                sub: [
                                    {
                                        id: "daan2_11f",
                                        text: "11F"
                                    },
                                    {
                                        id: "daan2_22f",
                                        text: "12F"
                                    },
                                    {
                                        id: "daan2_33f",
                                        text: "13F"
                                    }
                                ]
                            },
                            {
                                id: "daan3",
                                text: "Daan3",
                                sub: [{ id: "daan3_5f", text: "5F" }]
                            }
                        ]
                    },
                    {
                        id: "sinyi",
                        text: "Sinyi",
                        sub: [
                            { id: "sinyi1", text: "Sinyi1", sub: [] },
                            { id: "sinyi2", text: "Sinyi2", sub: [] },
                            { id: "sinyi3", text: "Sinyi3", sub: [] }
                        ]
                    },
                    { id: "wunshan", text: "Wunshan", sub: [] }
                ]
            },
            {
                id: "taichung",
                text: "Taichung",
                sub: [
                    { id: "south", text: "South", sub: [] },
                    { id: "west", text: "West", sub: [] },
                    { id: "north", text: "North", sub: [] }
                ]
            },

            {
                id: "kaohsiung",
                text: "Kaohsiung",
                sub: [
                    { id: "gushan", text: "Gushan", sub: [] },
                    { id: "zuoying", text: "Zuoying", sub: [] },
                    { id: "siaogang", text: "Siaogang", sub: [] }
                ]
            }
        ]
    },
    {
        id: "china",
        text: "China",
        sub: [
            { id: "hk", text: "Hong Kong", sub: [] },
            { id: "bj", text: "BeiJing", sub: [] },
            { id: "xm", text: "Xia Men", sub: [] }
        ]
    }
];

showOptions(level: number, refid?: string[]) {
    function deepTrace(
        areabase: AreaUnit[],
        targetLevel: number = 0,  // 目標level
        level: number = 0,        // 當前level
        refid?: string[]          // 比對的id
    ): AreaUnit[] | undefined {
        // 目標level小於當前level，不執行函數
        if (targetLevel < level) return;

        // 目標level和當前level相同
        if (targetLevel === level) {
            return areabase.map((item, index) => {
                let { id, text } = item;
                return { id, text };
            });
        } else {
            // 目標level和當前leval不相同
            for (let area of areabase) {
                if (area.id !== refid[level]) continue;
                return deepTrace(area.sub, targetLevel, level + 1, refid);
            }
            return;
        }
    }

    return deepTrace(this.Areas, level, 0, refid);
}

showCountries() {
    return this.showOptions(0);
}

showCities() {
    return this.showOptions(1, [this.reportFilterData.country]);
}

showRegions() {
    return this.showOptions(2, [
        this.reportFilterData.country,
        this.reportFilterData.city
    ]);
}

showSites() {
    return this.showOptions(3, [
        this.reportFilterData.country,
        this.reportFilterData.city,
        this.reportFilterData.region
    ]);
}

showFloors() {
    return this.showOptions(4, [
        this.reportFilterData.country,
        this.reportFilterData.city,
        this.reportFilterData.region,
        this.reportFilterData.site
    ]);
}