Adding 'input' used to edit array object key in selected elements - Vue.js

You might want to reconsider which component should be responsible of knowing which item is active at any point of time: hint: it should be the parent/consuming component. That is because you:

1. Have only a single input field, which means only one item can be edited at any point of time
2. You want to let the parent/consuming component to be the single source of truth of which item is actually active

Therefore, the first thing you should do is to ensure that isActive is a prop on the Item component, while the parent ItemList component keeps track of which is active at any point.

Then, it is simply a matter of:

• Implementing a toggling logic for the isActive flag. The flag is updated when a native click event is fired from the Item component. For the toggling logic, we can simply toggle between a zero-based index of the click item, or -1, which we used to indicate that nothing is active.
• Using v-bind:value and a computed property to reflect the value of the currently active item. We can simply retrieve it using this.items[this.activeIndex] on the parent component
• Listening to the onInput event and then updating the correct item

See proof-of-concept below:

Vue.component('item-list', {
  template: '#item-list-template',
  data() {
    return {
      items: [{
          title: 'item 1'
        },
        {
          title: 'item 2'
        },
        {
          title: 'item 3'
        },
        {
          title: 'item 4'
        },
        {
          title: 'item 5'
        },
        {
          title: 'item 6'
        }
      ],
      activeIndex: -1,
    }
  },
  methods: {
    onItemClick(index) {
      this.activeIndex = this.activeIndex === index ? -1 : index;
    },
    setActiveItemValue(event) {
      const foundItem = this.items[this.activeIndex];
      if (!foundItem) return;
      
      return this.items[this.activeIndex].title = event.currentTarget.value;
    }
  },
  computed: {
    activeItemValue() {
      return this.items[this.activeIndex]?.title ?? '';
    }
  }
});

Vue.component('item', {
  template: '#item-template',
  props: {
    isActive: Boolean,
    title: String
  }
});

new Vue({
  el: '#app'
});

li.active {
  background-color: yellow;
}

<script src="https://cdnjs.cloudflare.com/ajax/libs/vue/2.5.17/vue.js"></script>
<div id="app">
  <item-list></item-list>
</div>

<script type="text/x-template" id="item-list-template">
  <div>
    <input type="text" placeholder="Edit selected items" :value="activeItemValue" @input="setActiveItemValue" />
    <div class="items-col">
      <ul class="items-list">
        <item v-for="(item, i) in items" :key="i" :title="item.title" :isActive="activeIndex === i" @click.native="onItemClick(i)" />
      </ul>
    </div>
  </div>
</script>

<script type="text/x-template" id="item-template">
  <li class="item" :class="{ active: isActive }">{{ title }}</li>
</script>

If you want a solution with your current components (not the cleanest) , you can actually emit an event to the parent component when you activate an element that event should containe the index of the object in the items array

Then you can use the index to get and set the title variable , here is an example :

Item.vue

<template>
  <li class="item" @click="activateItem" :class="{ active: isActive }">{{ title }}</li>
</template>

<script>

export default {
  name: 'ItemsList',
  data() {
    return {
      isActive: false
    }
  },
  methods:{
    activateItem() {
      this.isActive = !this.isActive
      this.$emit('activatedItem', this.isActive ? this.index : null)
    }
  },
  props: {
    title: String,
    index: Number
  }
}
</script>

<style>
.item.active {
  color: red;
}
</style>

ItemList.vue

<template>
  <div>
    <input type="text" placeholder="Edit selected items" @input="inputChange" :value="inputValue"/>
    <div class="items-col">
      <ul class="items-list">
        <Item v-for="(item, index) in items" :key="index" :title="item.title" :index="index" @activatedItem="itemSelected"/>
      </ul>
    </div>
  </div>
</template>

<script>
import Item from '@/components/Item.vue'
export default {
  data() {
    return {
      items: [
        { title: 'item 1' },
        { title: 'item 2' },
        { title: 'item 3' },
        { title: 'item 4' },
        { title: 'item 5' },
        { title: 'item 6' }
      ],
      selectedIndex: null,
      inputValue: ''
    }
  },
  methods:{
    itemSelected(index){
        this.selectedIndex = index;
        if(this.selectedIndex != null) {
          this.inputValue = this.items[this.selectedIndex].title;
        }
    },
    inputChange(event){
      this.inputValue = event.target.value;
      if(this.selectedIndex != null){
        this.items[this.selectedIndex].title = this.inputValue
      }
    }
  },
  components: {
    Item
  }
}
</script>

You should also be aware that with the component Item you have given you can select more than one item !