Vue 如何使用props、emit实现自定义双向绑定的实现

import Vue from 'vueEsm' 

var Com = {
  name:'Com',
  props:['val'],
  template:`<input type='text' @input='handleInput'/>`,
  methods: {
    handleInput(e){
      this.$emit("input",e.target.value);
    }
  },
}

new Vue({
   el:'#app',
   data() {
     return {
       value:''
     }
   },
   components:{
    Com
   },
   template:`
   <div>
   <Com @input='post' :val='value'></Com>
   </div>
   `,
   methods:{
    post(data){
      this.value=data;
    }
   }
 })

<template>
 <div class="select">
  <div class="input" @click="collapse=!collapse">
   <span v-if="currentValue">{{currentLabel||currentValue}}</span>
   <span v-else class="placeholder">{{placeholder}}</span>

   <span :class="collapse?'arrow-down':'arrow-up'"></span>
  </div>

  <div class="option-list" v-show="!collapse">
   <div class="option-item" v-for="item in data" :key="item.id" @click="chooseItem(item)">{{item[itemLabel?itemLabel:'name']}}</div>
  </div>
 </div>
</template>

<script>
 export default {
  name: "mySelect",
  props: [
   'value',
   'placeholder',
   'data',
   'itemLabel',
   'itemValue'
  ],
  data() {
   return {
    collapse: true,
    currentValue: '',
    currentLabel: '',
   }
  },
  watch: {
   value: {
    immediate: true,
    handler(value) {
     this.currentValue = value;
     this.$emit('input', value);
     this.data.forEach(item => {
      if (item[this.itemValue ? this.itemValue : 'id'] == value) {
       return this.currentLabel = item[this.itemLabel ? this.itemLabel : 'name'];
      }
     });
    }
   },
   data:{
    immediate: true,
    handler(arr) {
     if(this.value||!this.currentLabel){
      arr.forEach(item=>{
       if(item[this.itemValue ? this.itemValue : 'id'] == this.value){
        this.currentLabel = item[this.itemLabel ? this.itemLabel : 'name'];
        return;
       }
      })
     }
    }
   }
  },
  methods: {
   chooseItem(item) {
    if (this.currentValue !== item[this.itemValue ? this.itemValue : 'id']) {
     this.$emit('change',item[this.itemValue ? this.itemValue : 'id']);
    }
    this.currentValue = item[this.itemValue ? this.itemValue : 'id'];
    this.currentLabel = item[this.itemLabel ? this.itemLabel : 'name'];
    this.$emit('input', this.currentValue);
    this.collapse = true;
   }
  }
 }
</script>

<style lang="scss" scoped>
 .select {
  position: relative;

  .input {
   width: 100%;
   height: 30px;
   line-height: 30px;
   background-color: #fff;
   border: 1px solid #02b4fe;
   border-radius: 0 3px 3px 0;
   padding-left: 10px;
   color: #666;
   position: relative;
   .placeholder {
    color: #aaa;
   }
  }

  .arrow-down {
   width: 0;
   height: 0;
   border-left: 5px solid transparent;
   border-right: 5px solid transparent;
   border-top: 8px solid #02b4fe;
   position: absolute;
   right: 5px;
   top: 10px;
  }

  .arrow-up {
   width: 0;
   height: 0;
   border-left: 5px solid transparent;
   border-right: 5px solid transparent;
   border-bottom: 8px solid #02b4fe;
   position: absolute;
   right: 5px;
   top: 10px;
  }

  .option-list {
   max-height: 200px;
   overflow-y: scroll;
   position: absolute;
   top: 2rem;
   left: 0;
   z-index: 5;
   width: 100%;
   padding: 0 5px;
   font-size: 10px;
   color: #aaa;
   background-color: #fff;
   text-align: left;
   box-shadow: 0 0 5px rgba(0, 0, 0, .1);
   border: 1px solid rgb(79, 192, 232);

   .option-item {
    text-align: center;
    line-height: 1.5rem;
   }
  }
 }
</style>

<template>
 <mySelect v-model="testValue" placeholder="请选择" :data="testArr" item-label="id"
           item-value="name"></mySelect>
</template>
<script>
  import mySelect from './mySelect'
  
  export default{
    components:{
     mySelect
    },
     data(){
      return {
         testValue:'',
         testArr:[]
       }
     },
     mounted(){
      //预置select的下拉选择基础数据，数据为对象数组，包含id和name属性
     }
}
</script>