子传父 : 普通形式

父组件 : 

<template>
  <div class="app">
    <h2>当前计数: {{ counter }}</h2>

    <!-- 并且监听内部的sub事件 -->
    <sub-counter @sub="subBtnClick"></sub-counter>
  </div>
</template>

<script>
  import SubCounter from './SubCounter.vue'

  export default {
    components: {
      SubCounter
    },
    data() {
      return {
        counter: 0
      }
    },
    methods: {
      subBtnClick(count) {
        this.counter -= count
      }
    }
  }
</script>

<style scoped>
</style>

子组件 : 

<template>
  <div class="sub">
    <button @click="btnClick(1)">-1</button>
    <button @click="btnClick(5)">-5</button>
    <button @click="btnClick(10)">-10</button>
  </div>
</template>

<script>
  export default {
    methods: {
      btnClick(count) {
        this.$emit("sub", count)
      }
    }
  }
</script>

<style scoped>
</style>