初始化子组件后，将子组件的值传递给父组件

<!-- 父组件 -->
<template>
  <div>
    <child-component :value="childValue"></child-component>
  </div>
</template>

<script>
import ChildComponent from './ChildComponent.vue';

export default {
  components: {
    ChildComponent
  },
  data() {
    return {
      childValue: 'Hello World'
    };
  }
};
</script>

<!-- 子组件 -->
<template>
  <div>
    <p>{{ value }}</p>
  </div>
</template>

<script>
export default {
  props: ['value']
};
</script>

<!-- 父组件 -->
<template>
  <div>
    <child-component @valueChange="handleValueChange"></child-component>
  </div>
</template>

<script>
import ChildComponent from './ChildComponent.vue';

export default {
  components: {
    ChildComponent
  },
  methods: {
    handleValueChange(value) {
      console.log(value);
    }
  }
};
</script>

<!-- 子组件 -->
<template>
  <div>
    <button @click="emitValue">传递值给父组件</button>
  </div>
</template>

<script>
export default {
  methods: {
    emitValue() {
      const value = 'Hello World';
      this.$emit('valueChange', value);
    }
  }
};
</script>