Problem

I have a component with data function that returns an object:

data() => ({
    car: {}
})

Car is an empty string, then I want to add values by some interaction (button click):

<div>
    <p>{{ car }}</p>
    <button @click="addProps">add props</button>
</div>

...
methods: {
    addProps() {
        this.car.brand = 'Kia'
    }
}

Then if I click the button the "car" would not be updated in the UI, this is the reactivity problem, Vue add a specific method to solve this problem using "$set":

...
methods: {
    addProps() {
        this.$set(this.car, 'car', 'Kia' )
    }
}

This is helpful if you have only one property to add, but in many cases is necessary to add more than one property, in this case JS has a function to solve this problem by assing to the same data attribute a new assing object:

methods: {
    addProps() {
        this.$set(this.car, 'brand', 'Kia' )
        this.car = Object.assign({}, this.car, {
            'brand': 'Kia',
            'year': '2020'
        })
    }
}

That's all thanks for reading.