Vue Js Checkbox Select all

createApp({
    data() {
      return {
      country:[
               {
                'id':'1',
                'countryName':'AMERICA'
              },
              {
               'id':'2',
               'countryName':'AUSTRALIA'
              },
              {
               'id':'3',
               'countryName':'INDIA'
             },
             {
               'id':'4',
               'countryName':'ENGLAND'
             }
            ],
          checked:[]
         
        }
    },
    computed: {
        checkAll: {
            get: function () {
                return this.country ? this.checked.length == this.country.length : false;
            },
            set: function (value) {
                var checked = [];
                if (value) {
                    this.country.forEach(function (c) {
                        checked.push(c.countryName);
                    });
                }
                this.checked = checked;
            }
        }
    }
}).mount('#app')
</script>