mutation.js

import Vue from 'vue';
import Vuex from 'vuex';

Vue.use(Vuex);

export const store = new Vuex.Store({

    state: {
        counter: 0
    },

    getters: {
        /**
         * access counter in state from the paramater 
         */
        addCurrencyToCounter: function (state) {
            return `$ ${state.counter} (dollars)`;
        },

        incrementCounterByTen: function(state) {
            return state.counter + 10
        }
    },

    mutations: {
        increase: function(state) {
            state.counter ++;
        },

        decrement: function(state) {
            state.counter++;
        }
    }
});