passing data from child to parent component in Vue

问题

I am practicing Vue JS and would like to understand how to pass data from a child component to a parent component emitting an event. This is my parent component BookList:

<template>
  <div class="booklist">
    <BookForm @book-is-created="onClickForm" />
    <table  v-for="book in books">
      <tr>
        <th> Author </th>
        <th> Title </th>
        <th> Publishing House </th>
        <th> Edition Date </th>
      </tr>
      <tr>
        <td> {{ book.author}}</td>
        <td> {{ book.title}}</td>
        <td> {{ book.publishing_house}}</td>
        <td> {{ book.edition_date}}</td>
      </tr>
    </table>
  </div>
</template>
<script>
import BookForm from './BookForm';
export default {
  name: 'hello',
  data: () => ({
    books: []
  }),
    mounted() {
      axios.get("http://localhost:3000/api/v1/books")
      .then(response => {this.books = response.data})
    },
    components:{
      BookForm
    },
    methods:{
      onClickForm(){
        console.log(this.book)
        console.log('Book created')
      }
    }
  }
</script>

Here's the code of my BookForm component from which I would enter the book data and update the BookList emitting the 'book-is-created' and the book object:

<template lang="html">
  <form>
      <label for="author">Author</label>
      <input v-model="book.author"type="text" name="author" value="">
      <br>
      <label for="title">Title</label>
      <input v-model="book.title" type="text" name="title" value="">
      <br>
      <label for="publishing_house">Publishing house</label>
      <input v-model="book.publishing_house" type="text" name="publishing_house" value="">
      <br>
      <label for="edition_date">Edition Date</label>
      <input v-model="book.edition_date" type="text" name="edition_date" value="">
      <br>
      <button v-on:click.prevent="createBook" >createBook</button>
  </form>
</template>

<script>
export default {
  data:() =>({
    book:{
      author:"",
      title:"",
      publishing_house: "",
      edition_date: ""
    }
  }),
  methods:{
    createBook: function() {
      //console.log(this.book)
      this.$emit('book-is-created', this.book)
    }
}
}
</script>

When try to console log the book object it returns 'undefined'. How can I make available the book object in the BookList component in order to update my list?

回答1:

The code is passing book as a parameter for the book-is-created event, but your handler is not accepting that parameter. All you need to do is add book as a parameter to your handler and you will be able to use it inside the method.

methods:{
  onClickForm(book){
    console.log(book)
    console.log('Book created')
    // this.books.push(book)
  }
}

As a side note, avoid defining data with arrow functions. Your current code is ok, but if you ever tried to use this inside your data function, this would refer to the wrong thing. Just use a typical function or the new method syntax.

data(){
   return {
      book:{
        author:"",
        title:"",
        publishing_house: "",
        edition_date: ""
      }
   }
}

来源：https://stackoverflow.com/questions/44088646/passing-data-from-child-to-parent-component-in-vue