Deleting vue component from list always delete the last element in list

Asked By: Anonymous

I have read the documentation for rendering the custom components in list using v-for here.

But for some reason, I am not able to get this working.It always delete the last component instead of the one I send in the index. Any idea why it is not working ?

My VUE JS version is : 2.5.16.

Using PHPStorm IDE and running on docker (linux container)

And Laravel mix (I have “laravel-mix”: “0.*” entry in package.json) to use webpack and compile the JS modules.

Here is the piece of some of my code

// Parent Component JS
<template>
    <ul>
        <li
            is="child-component"
            v-for="(child, index) in componentList"
            :key="index"
            :myVal="Something...."
            @remove="dropField(index)"
            @add-custom-field="addField"
        ></li>
    </ul>
</template>

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

    export default {
        name: 'CustomList',

        components: {'child-component' :childComponent},

          data() {
            return {
                componentList: []
            }
          },

       methods: {
            addField() {
                console.log('Handling add-custom-field  field...');
                this.componentList.push(childComponent);
            },

            dropField(index) {
                console.log(`I am deleting the component with index = ${index}  from listview in parent...`);
                this.componentList.splice(index, 1); 
            }
        }
    }


// Child Component JS

<template>
    <div>
       <input type="text" v-model="currentValue" /><button @click.prevent="$emit('remove')" > Remove </button>
    </div
</template>
<script>
  export default {
     props: { myVal : '' },
     data() { return { currentValue: ''} },
     created() {this.currentValue = this.myVal;}

  }
</script>

Solution

Answered By: Anonymous

The issue is caused by in-place patch” strategy for v-for. That means Vue will not rebuild all childs when removed one element from componentList.

Check Vue Guide on an “in-place patch” strategy for v-for:

When Vue is updating a list of elements rendered with v-for, by
default it uses an “in-place patch” strategy. If the order of the data
items has changed, instead of moving the DOM elements to match the
order of the items, Vue will patch each element in-place and make sure
it reflects what should be rendered at that particular index.

Actually you already deleted the last item, but the problem is the data property=currentValue of first&second child have been ‘a’, ‘b’, when first mounted. Later when Vue re-render (delete the last child), data property=currentValue keeps same value though prop=myVal already changed.

Look at below demo, I added one input and bind myVal, you will see the differences.

Vue.config.productionTip = false_x000D_
_x000D_
let childComponent = Vue.component('child', {_x000D_
  template: `<div class="item">_x000D_
      <p>Index:{{parentIndex}} => <button @click.prevent="removed()" > Remove </button>_x000D_
      Data:<input type="text" v-model="currentValue" />Props:<input type="text" v-bind:value="myVal" />_x000D_
      </p>       _x000D_
    </div>`,_x000D_
     props: { 'myVal':{_x000D_
          type: String,_x000D_
          default: ''_x000D_
        } ,_x000D_
        'parentIndex': {_x000D_
          type: Number,_x000D_
          default: 0_x000D_
        }_x000D_
      },_x000D_
     data() {_x000D_
       return { _x000D_
        currentValue: ''_x000D_
       } _x000D_
     },_x000D_
     mounted() {_x000D_
      this.currentValue = this.myVal_x000D_
     },_x000D_
     methods: {_x000D_
      removed: function () {_x000D_
        this.$emit('remove')_x000D_
      }_x000D_
     }_x000D_
})_x000D_
_x000D_
_x000D_
app = new Vue({_x000D_
  el: "#app",_x000D_
  data() {_x000D_
    return {_x000D_
        componentList: ['a', 'b', 'c'],_x000D_
        componentType:childComponent_x000D_
    }_x000D_
  },_x000D_
_x000D_
  methods: {_x000D_
    addField() {_x000D_
        console.log('Handling add-custom-field  field...');_x000D_
        this.componentList.push(childComponent);_x000D_
    },_x000D_
_x000D_
    dropField(index) {_x000D_
        console.log(`I am deleting the component with index = ${index}  from listview in parent...`);_x000D_
        this.componentList.splice(index, 1); _x000D_
    }_x000D_
  }_x000D_
})

li:nth-child(odd) {_x000D_
  background-color:#d0d5dd;_x000D_
}

<a href="https://unpkg.com/[email protected]/dist/vue.js">https://unpkg.com/[email protected]/dist/vue.js</a>_x000D_
<div id="app">_x000D_
    <ul>_x000D_
        <li v-for="(child, index) in componentList"><div_x000D_
            :is="componentType"_x000D_
            :key="index"_x000D_
            :my-val="child"_x000D_
            :parent-index="index"_x000D_
            @remove="dropField(index)"_x000D_
            @add-custom-field="addField"_x000D_
        >{{child}}</div></li>_x000D_
    </ul>_x000D_
</div>

x000D