[Vue warn]: Avoid mutating a prop directly since the value will be overwritten whenever the parent component re-renders. Instead, use a data or computed property based on the prop's value. Prop being mutated: "value"

Vue.component("RxSelect", {
 model: {
 prop: "value",
 event: "change",
 },
 props: {
 value: [Number, String],
 map: Map,
 },
 template: `
  <select
   v-model="value"
   @change="$emit('change', value)"
  >
   <option
   v-for="[k,v] in map"
   :value="k"
   :key="k"
   >{{v}}</option>
  </select>
  `,
});

<main id="app">
 当前选择的性别是: {{map.get(sex)}}
 <div>
 <rx-select :map="map" v-model="sex" />
 </div>
</main>

new Vue({
 el: "#app",
 data: {
 map: new Map().set(1, "保密").set(2, "男").set(3, "女"),
 sex: "",
 },
});

Vue.component("RxSelect", {
 model: {
 prop: "value",
 event: "change",
 },
 props: {
 value: [Number, String],
 map: Map,
 },
 data() {
 return {
  innerValue: this.value,
 };
 },
 watch: {
 value(val) {
  this.innerValue = val;
 },
 innerValue(val) {
  this.$emit("change", val);
 },
 },
 template: `
 <select v-model="innerValue">
 <option
  v-for="[k,v] in map"
  :value="k"
  :key="k"
 >{{v}}</option>
 </select>
 `,
});

Vue.component("RxSelect", {
 model: {
 prop: "value",
 event: "change",
 },
 props: {
 value: [Number, String],
 map: Map,
 },
 computed: {
 innerValue: {
  get() {
  return this.value;
  },
  set(val) {
  this.$emit("change", val);
  },
 },
 },
 template: `
 <select v-model="innerValue">
 <option
  v-for="[k,v] in map"
  :value="k"
  :key="k"
 >{{v}}</option>
 </select>
 `,
});