reactive.vue

<script>
export default {
  data: function() {
    return {
     disp_menu: [true, false, false]
    }
  },
  methods: {
    changeMenu(num) {
      const index = num;
      for (var i = 0; i < this.disp_menu.length; i++) {
        this.disp_menu.splice(i, 1, false);
      }
      this.disp_menu.splice(index, 1, true);
      console.log(this.disp_menu);
    }
  }
}
</script>