vue使用$emit时,父组件无法监听到子组件的事件实例

<div id="counter-event-example">  <p>{{ total }}</p>  <button-counter v-on:ee="incrementTotal"></button-counter>  <button-counter v-on:eEvent="incrementTotal"></button-counter>  <child ref="cmpSelect" v-on:ee="incrementTotal" option-api-url="/api/admin/cms/cmsCategory/getOptions.do"></child> </div> <script>  Vue.component('button-counter', {   template: '<button v-on:click="increment">{{ counter }}</button>',   data: function () {    return {     counter: 0    }   },   methods: {    increment: function () {     this.counter += 1     this.$emit('ee', this.counter);//有效     this.$emit('eEvent', this.counter);//无效，不能使用大写的驼峰规则命名    }   },  })  new Vue({   el: '#counter-event-example',   data: {    total: '点击下面的按钮'   },   methods: {    incrementTotal: function (b) {     this.total = b;    }   }  }) </script>