Reactive Window Parameters in Vue.js - Adapted from: https://blog.usejournal.com/reactive-window-parameters-in-vuejs-fc5de75d7ab5

WindowInstanceMap.js

import Vue from 'vue'

export default class extends Vue {
  constructor() {
    super({
      data() {
        return {
          scrollY: 0
        }
      },
      created() {
        window.addEventListener('scroll', e => {
          this.scrollY = window.scrollY
        })
      },
    })
  }
}

This version of WindowInstanceMap.js from James Wee requires you to instantiate the class so that you don't have seemingly unused imports:

// App.js
import WindowInstanceMap from './WindowInstanceMap.js'
new WindowInstanceMap()

This would make it a much preferred solution since seemingly unused imports can be removed either by automatic processes or human beings unaware of the details of the import.