Computed property was assigned to but it has no setter - a toggle component

Question

I am creating a simple switch toggle component in Vue where it has a v-model and @updated. But I can't seem to change the model when the user toggles the switch. First I was getting the error to avoid mutating a prop directly. But now I am getting another error.

[Vue warn]: Computed property "isSwitchOn" was assigned to but it has no setter.

The component is meant to be used like this

<iswitch v-model="switchGender" @updated="handleUpdatedGender" />

Here is the component itself

export default {
    template: `
        <span
            @click="toggleSwitch"
            :class="{ active: isSwitchOn }">

            <span class="toggle-knob"></span>
        </span>
    `,

    props: ['value'],

    methods:
    {
        toggleSwitch()
        {
            this.isSwitchOn = !this.isSwitchOn

            this.$emit('input', this.isSwitchOn)
            this.$emit('updated')
        }
    },

    computed:
    {
        isSwitchOn()
        {
            return this.value
        }
    },
};

Answer 1

The error is triggered by this statement: this.isSwitchOn = !this.isSwitchOn. You are trying to assign a value to a computed property but you didn't provide a setter.

You need to define your computed property as follow for it to work as a getter and a setter:

computed:
{
    isSwitchOn:
    {
        get()
        {
            return this.value
        },
        set(value)
        {
            this.value = value
        }
    }
}

Also, it is not advised to mutate a prop directly. What you could do is to add a new data property and sync it with the value prop using a watcher.

I think something like this will work:

props: ['value'],
data()
{
    return {
       val: null
    }
},
computed:
{
    isSwitchOn:
    {
        get()
        {
            return this.val
        },
        set(value)
        {
            this.val = value
        }
    }
},
watch: {
   value(newVal) {
       this.val = newVal
   }
}

Answer 2

Computed properties are by default getter-only, but you can also provide a setter when you need it. Check official documentation

computed:
{
    isSwitchOn() {
        get() { return this.value }
        set(val) { this.value = val }
    }
}

Alternative way:

In your parent component:

<iswitch ref="switcher" @input="methodForInput" v-model="switchGender" @updated="handleUpdatedGender" />

methods: {
  methodForInput(event){
    this.$refs.switcher.isSwitchOn = event;
  }
}

In your child component:

export default {
    template: `
        <span
            @click="toggleSwitch"
            :class="{ active: isSwitchOn }">

            <span class="toggle-knob"></span>
        </span>
    `,

    data() {
      return {
        isSwitchOn: false
      };
    },

    methods:
    {
        toggleSwitch()
        {
            this.isSwitchOn = !this.isSwitchOn

            this.$emit('input', this.isSwitchOn)
            this.$emit('updated')
        }
    }
};

Updates 3: Sorry, didn't include parent component at first.