In Vue3, how to make Custom Component work with v-model for group of checkboxs?

Question

The below given code you can see the magic of v-model, after checking / unchecking the checkboxes the array checkedNames will add/remove names automatically. We don't have to write anything to push/slice/filter names from the array, right?

const { ref } = Vue;

const App = {
  setup () {
    const checkedNames = ref([])
    return { checkedNames }
  }
}

Vue.createApp(App).mount("#app");

<script src="https://unpkg.com/vue@3.0.11/dist/vue.global.js"></script>

<div id="app">
  <input type="checkbox" id="jack" value="Jack" v-model="checkedNames">
  <label for="jack">Jack</label>
  <input type="checkbox" id="john" value="John" v-model="checkedNames">
  <label for="john">John</label>
  <input type="checkbox" id="mike" value="Mike" v-model="checkedNames">
  <label for="mike">Mike</label>
  <br>
  <span>Checked names: {{ checkedNames }}</span>
</div>

My question is: How can I do the same feature but with custom components?

You can see, In below given code snippets I tried but I did not like it because we are missing that magic of v-model instead I am handeling this in my function addOrRemoveItem()

heads-up: It may seem to you that I am over explaining :) sorry for that.

I followed this tutorial for some idea but was not much helpful, then referred vue official doc here. below is the functional code but it's kinda overkill.

const { ref, createApp } = Vue;

const app = createApp({
  setup() {
    const itemsSelected = ref([]);
    const items = ref([
      { id: '1', name: 'Jack' }, 
      { id: '2', name: 'John' }, 
      { id: '3', name: 'Mike' }, 
    ]);

    const addOrRemoveItem = (itemId) => {
      const exists = itemsSelected.value.includes(itemId);

      if (exists) {
        itemsSelected.value = itemsSelected.value.filter((id) => id !== itemId);
      } else {
        itemsSelected.value.push(itemId);
      }
    };

    return { 
      items,
      itemsSelected,
      addOrRemoveItem,
    };
  },
});

app.component('custom-checkbox', {
   props: {
    item: { type: Object, default: () => ({}) },
    modelValue: { type: Array, default: () => [] },
  },
  template: `
    <div>
      <input
        type="checkbox" :value="item.id"
        @change="$emit('update:model-value', $event.target.checked)"
      > {{ item.name }}
    </div>
    `
})

app.mount("#app");

<script src="https://unpkg.com/vue@3.0.11/dist/vue.global.js"></script>

<div id="app">
  <div><code>itemsSelected: {{ itemsSelected }}</code></div>
 <hr />
  <custom-checkbox
    v-for="item in items"
    :key="item.id"
    :item="item"
    :model-value="itemsSelected"
    @update:model-value="addOrRemoveItem(item.id)"
  ></custom-checkbox>
</div>

As mentioned above, the code was bit overkill when I follow as mentioned in doc $emit('update:model-value', ...) which can be simply anything for eg: $emit('val-updated'), here is bit simplified version after removing unwanted prop and reducing the length of $emit.

const { ref, createApp } = Vue;

const app = createApp({
  setup() {
    const itemsSelected = ref([]);
    const items = ref([
      { id: '1', name: 'Jack' }, 
      { id: '2', name: 'John' }, 
      { id: '3', name: 'Mike' }, 
    ]);

    const addOrRemoveItem = (itemId) => {
      const exists = itemsSelected.value.includes(itemId);

      if (exists) {
        itemsSelected.value = itemsSelected.value.filter((id) => id !== itemId);
      } else {
        itemsSelected.value.push(itemId);
      }
    };

    return { 
      items,
      itemsSelected,
      addOrRemoveItem,
    };
  },
});

app.component('custom-checkbox', {
   props: {
    item: { type: Object, default: () => ({}) },
  },
  template: `
    <div>
      <input
        type="checkbox" :value="item.id"
        @change="$emit('val-updated')"
      > {{ item.name }}
    </div>
    `
})

app.mount("#app");

<script src="https://unpkg.com/vue@3.0.11/dist/vue.global.js"></script>

<div id="app">
  <div><code>itemsSelected: {{ itemsSelected }}</code></div>
 <hr />
  <custom-checkbox
    v-for="item in items"
    :key="item.id"
    :item="item"
    @val-updated="addOrRemoveItem(item.id)"
  ></custom-checkbox>
</div>

Answer 1

The addOrRemoveItem() method is not needed at all. Just let the default Vue v-model logic for a checkbox do the heavy lifting. Only thing you need is to use computed prop for a v-model (because using prop directly is not possible as props can not be mutated from child component)

const {
  ref,
  createApp
} = Vue;

const app = createApp({
  setup() {
    const itemsSelected = ref([]);
    const items = ref([{
        id: '1',
        name: 'Jack'
      },
      {
        id: '2',
        name: 'John'
      },
      {
        id: '3',
        name: 'Mike'
      },
    ]);

    return {
      items,
      itemsSelected,
    };
  },
});

app.component('custom-checkbox', {
  props: {
    item: {
      type: Object,
      default: () => ({})
    },
    modelValue: {
      type: Array,
      required: true
    }
  },
  emits: ['update:modelValue'],
  computed: {
    model: {
      get() {
        return this.modelValue
      },
      set(value) {
        this.$emit('update:modelValue', value)
      }
    }
  },
  template: `
    <div>
      <input
        type="checkbox" :value="item.id" v-model="model"
      > {{ item.name }}
    </div>
    `
})

app.mount("#app");

<script src="https://unpkg.com/vue@3.0.11/dist/vue.global.js"></script>

<div id="app">
  <div><code>itemsSelected: {{ itemsSelected }}</code></div>
  <hr />
  <custom-checkbox v-for="item in items" :key="item.id" :item="item" v-model="itemsSelected"></custom-checkbox>
</div>