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

Question

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>

Answer 1

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

let childComponent = Vue.component('child', {
  template: `<div class="item">
      <p>Index:{{parentIndex}} => <button @click.prevent="removed()" > Remove </button>
      Data:<input type="text" v-model="currentValue" />Props:<input type="text" v-bind:value="myVal" />
      </p>       
    </div>`,
     props: { 'myVal':{
          type: String,
          default: ''
        } ,
        'parentIndex': {
          type: Number,
          default: 0
        }
      },
     data() {
       return { 
        currentValue: ''
       } 
     },
     mounted() {
      this.currentValue = this.myVal
     },
     methods: {
      removed: function () {
        this.$emit('remove')
      }
     }
})


app = new Vue({
  el: "#app",
  data() {
    return {
        componentList: ['a', 'b', 'c'],
        componentType:childComponent
    }
  },

  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); 
    }
  }
})

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

<script src="https://unpkg.com/vue@2.5.16/dist/vue.js"></script>
<div id="app">
    <ul>
        <li v-for="(child, index) in componentList"><div
            :is="componentType"
            :key="index"
            :my-val="child"
            :parent-index="index"
            @remove="dropField(index)"
            @add-custom-field="addField"
        >{{child}}</div></li>
    </ul>
</div>

Answer 2

I discover that if you have another updated :key property (not index) it will work as you want

here's my example

<template>
    <div id="app">
        <ul>
            <li
                v-for="(teacher, index) in teachers_list"
                v-bind="teacher"
                :key="teacher.id"
            >
            <p>Teacher id {{teacher.id}}</p>
            <button @click="deleteTeacher(index)"></button>
            </li>
        </ul>
    </div>
</template>

<script>
export default {
    data() {
        return {
                teachers_list: [
                {name: 'teacher a', id: 100},
                {name: 'teacher b', id: 200},
                {name: 'teacher c', id: 300},
            ]
        }
    },
    methods: {
        deleteTeacher(index) {
            console.log(index);

            this.teachers_list.splice(index, 1)
        }
    }
}
</script>