const numberOfDrinksSold = Symbol(numberOfDrinksSold); return ({ on: { click: function (e) { alert(this.dataset.drinkSelection + ' coming right up!'); this[numberOfDrinksSold]++; } }, props: { [numberOfDrinksSold]: 0 }, methods: { onPropsChange: function () { console.log('Thanks, Rosmerta'); } }, vals: { title: 'Clicker' } });