vue三级联动，不发ajax请求

<template>    <div class="city-select" id="city">        <select v-model="selectedProvince" name="province">            <option v-for="(item, index) in provinces"                    v-if="item.level === 1"                    :value="item">                {{ item.name }}      </option>        </select>        <select v-model="selectedCity" name="city">            <option                    v-for="(item, index) in cities"                    :value="item">                {{ item.name }}      </option>        </select>        <select v-model="selectedBlock" name="block">            <option                    v-for="(item, index) in blocks"                    :value="item">                {{ item.name }}      </option>        </select>    </div></template><script>    import provinces from ‘./../../assets/js/city‘    import Vue from ‘vue‘    export default {        name: ‘city‘,        created() {            // 数据初始化,默认选中北京市,默认选中第一个;北京市数据为总数据的前18个            let beijing = this.provinces.slice(0, 19);            this.cities = beijing.filter(item => {                if (item.level === 2) {                    return true                }            });            this.selectedCity = this.cities[0];            this.blocks = beijing.filter(item => {                if (item.level === 3) {                    return true                }            });            this.selectedBlock = this.blocks[0]        },        watch: {            selectedProvince(newVal, oldVal) {                // 港澳台数据只有一级,特殊处理                if (newVal.sheng === ‘71‘ || newVal.sheng === ‘81‘ || newVal.sheng === ‘82‘) {                    this.cities = [newVal];                    this.blocks = [newVal]                } else {                    this.cities = this.provinces.filter(item => {                        if (item.level === 2 && item.sheng && newVal.sheng === item.sheng) {                            return true                        }                    })                }                var _this = this;                // 此时在渲染DOM,渲染结束之后再选中第一个                Vue.nextTick(() => {                    _this.selectedCity = _this.cities[0];                    _this.$emit(‘input‘, _this.info)                })            },            selectedBlock() {                var _this = this;                Vue.nextTick(() => {                    _this.$emit(‘input‘, _this.info)                })            },            selectedCity(newVal) {                // 选择了一个市,要选择区了 di是城市的代表,sheng                if (newVal.sheng === ‘71‘ || newVal.sheng === ‘81‘ || newVal.sheng === ‘82‘) {                    this.blocks = [newVal];                    this.cities = [newVal]                } else {                    this.blocks = this.provinces.filter(item => {                        if (item.level === 3 && item.sheng && item.sheng == newVal.sheng && item.di === newVal.di && item.name !== ‘市辖区‘) {                            return true                        }                    })                }                var _this = this;                Vue.nextTick(() => {                    _this.selectedBlock = _this.blocks[0];                    // 触发与 v-model相关的 input事件                    _this.$emit(‘input‘, _this.info)                })            }        },        computed: {            info() {                return {                    province: this.selectedProvince,                    city: this.selectedCity,                    block: this.selectedBlock                }            }        },        data() {            return {                selectedProvince: provinces[0],                selectedCity: 0,                selectedBlock: 0,                cities: 0,                provinces,                blocks: 0            }        }    }</script>city.js部分格式