Getting error $state not defined in vuejs

Hello I am working with Vuejs. I have defined a global variable using the following code in main.js

Vue.prototype.$state = Vue.observable({ val: 1 });

In another file I want to access this variable inside script so I am using

export default {
methods: {
    showup() {
      if ($state.val === 2) $state.val = 1; else $state.val = 2;
    },
  },

But I am getting the error as

54:11  error  '$state' is not defined  no-undef

Can someone help me with this. Thanks a lot .

>Solution :

You missed to add this which refers to the Vue instance :

export default {
methods: {
    showup() {
      if (this.$state.val === 2) this.$state.val = 1; else this.$state.val = 2;
    },
  },