vuejs computed with parameter code example

Example 1: cannot access this from computed vuejs

computed:{
                // Get data from vuex
                $currency(){
                    return this.$store.state.currency
                }
            },

Example 2: computed vue js

var vm = new Vue({
  el: '#demo',
  data: {
    firstName: 'Foo',
    lastName: 'Bar',
    fullName: 'Foo Bar'
  },
  watch: {
    firstName: function (val) {
      this.fullName = val + ' ' + this.lastName
    },
    lastName: function (val) {
      this.fullName = this.firstName + ' ' + val
    }
  }
})