element + vue3，级联选择器实现省市区

 由于es6支持哈希，所以数据量只要不太大，就不需要对el-cascader进行点击后在调接口出现下一级，很简单的就是直接获取所有数据。

<template>
    <div>
        <el-cascader :modelValue="modelValue" :props="innerProps" :options="options" @change="handleChange" filterable
            :show-all-levels="showAllLevels" :disabled="disabled" :placeholder="placeholder" :clearable="clearable"
            style="width:100%" @blur="onBlur" @focus="onFocus" @close="handleClose" @visible-change="onVisibleChange" />
        <!-- --- {{ modelValue }} -->
    </div>
</template>

<script lang="ts" setup>
import { ref, reactive, toRaw, onMounted, watch, onBeforeUnmount } from 'vue'
import type { CascaderProps } from 'element-plus'
import * as api from "./api.js";

const props = defineProps({
    modelValue: {
        type: Array,
        default: []
    },
    // 是否支持清空选项
    clearable: {
        type: Boolean,
        default: true,
    },
    // 是否多选
    // multiple: {
    //     type: Boolean,
    //     default: false,
    // },
    // 指定某省，传入该自治区的areacode
    designation: {
        type: String,
        default: '',
    },
    // 仅显示最后一级
    showAllLevels: {
        type: Boolean,
        default: true,
    },
    // 是否禁用
    disabled: {
        type: Boolean,
        default: false,
    },
    // 输入框占位文本
    placeholder: {
        type: String,
        default: '',
    },
    // 是否选择任意一级选项，还是最后叶子结点
    checkStrictly: {
        type: Boolean,
        default: true,
    },
    // 次级菜单的展开方式,click和hover
    expandTrigger: {
        type: String,
        default: 'click',
    },
    // 多选个数限制selectNum
    multipleSelectNum: {
        type: Number,
        default: 1,
    },
     // 省市县乡镇，显示层级，默认为2，到区县。0为省，1为市，2为区县，3为乡镇
     level: {
        type: Number,
        default: 2,
    },
})

let options: any = ref([])  //树
const watchArr = ref([])

onMounted(() => {
    // 获取全量数据
    getAllData()
})

//重新定义一个值来接受prop
const isMultiple = ref(false)

//因为prop中的值非动态响应，所以需要通过watch监听，immediate 初始化时接收父组件中的传值
watch(() => props.multipleSelectNum, () => {
    // isMultiple.value = props.multipleSelectNum;
    if(props.multipleSelectNum > 1) {
        isMultiple.value = true
    }
    console.log(isMultiple.value,props.multipleSelectNum,'---props.multipleSelectNum;');
    
}, {
    immediate: true
})

onBeforeUnmount(() => {})

const emit = defineEmits(['update:modelValue', 'change'])
const handleChange = (e: any, e2: any) => {
    watchArr.value = e
    emit('change', e)
    emit('update:modelValue', e)
}

async function getAllData() {
    let res = await api.SearchAdministrativeDivisions({
        queryArea: props.designation,
        level: props.level
    })
    options.value = res.data
}

function onFocus(e: any) { }
async function onBeforeFilter(e: any) {
    let res = await api.SearchAdministrativeDivisions({
        queryArea: e
    })
    const fn = (arr: any[]) => {
        arr.forEach((item, index) => {
            if (item.children && item.children.length) {
                item.children = fn(item.children)
            } else {
                if (item.children) delete item.children
            }
        })
        return arr
    }
    // console.log(options, '---options');
    options.value = fn(res.data)
}
// const isMultiple = ref(false)
const innerProps: CascaderProps = {
    checkStrictly: props.checkStrictly,
    // lazy: true,
    value: 'areaCode',
    label: 'name',
    multiple: isMultiple.value, //modify
    expandTrigger: props.expandTrigger,
}
const handleClose = () => { }
const onBlur = () => {
    // console.log('---onBlur');
}
const onVisibleChange = (e: any) => {
    // if (props.modelValue.length < props.multipleSelectNum && props.multiple == true) {
        if (props.modelValue.length < props.multipleSelectNum && isMultiple.value == true) { //modify
        function onRabbit(list: any) {
            list.forEach((el: any) => {
                if (el.children && el.children.length > 0) {
                    el.children = onRabbit(el.children);
                }
                el.disabled = false;
                el.isFlag = false
            });
            return list;
        }
        const newList = onRabbit(options.value);
        options.value = newList;
    }
}
// 监听
watch(
    () => watchArr.value,
    (newVal, oldVal) => {
        // if (props.multiple == true) {
            if (isMultiple.value == true) {   //modify
            // console.log(oldVal,`watch监听变化前的数`)
            // console.log(newVal, `watch监听变化后的数据`)
            if (newVal.length >= props.multipleSelectNum) {
                function onRabbit(list: any) {
                    list.forEach((el: any) => {
                        if (el.children && el.children.length > 0) {
                            el.children = onRabbit(el.children);
                        }
                        newVal.forEach((v: any) => {
                            if (v[v.length - 1] != el.areaCode) {
                                if (el.isFlag) {
                                } else {
                                    el.disabled = true
                                    el.isFlag = true
                                }
                            } else {
                                el.disabled = false
                                el.isFlag = true
                            }
                        })
                    });
                    return list;
                }
                const newList = onRabbit(options.value);
                options.value = newList;
            } else {
                function onRabbit(list: any) {
                    list.forEach((el: any) => {
                        if (el.children && el.children.length > 0) {
                            el.children = onRabbit(el.children);
                        }
                        el.disabled = false;
                        el.isFlag = false
                    });
                    return list;
                }
                const newList = onRabbit(options.value);
                options.value = newList;
            }
        }
    },
    {
        immediate: true, // 立即执行
        deep: true // 深度监听
    }
)
</script>
  
<style></style>