SOURCE

Vue.component('my-component', {
  template: `
  <div>
    <p>propA: {{ propA }}</p>
    <p>val: {{ val }}</p>
  </div>
  `,
  computed: {
    val: {
      get: function () {
        console.log(this.propA)
        return this.propA
      },
      set: function (val) {
        console.log('setter execute')
        console.log(val)
      }
    }
  },
  props: ['propA'],
  mounted: function () {
    setTimeout(() => {
      this.val = 1000
    }, 2000);
  }
})
new Vue({
  el: "#app",
  data: {
    a: 1
  }
})

<div id="app">
  <my-component :prop-a="a"></my-component>
</div>