om/node_modules/vuetify/src/mixins/stackable.ts

import Vue from 'vue'

import { getZIndex } from '../util/helpers'

interface options extends Vue {
  $refs: {
    content: Element
  }
}

/* @vue/component */
export default Vue.extend<options>().extend({
  name: 'stackable',

  data () {
    return {
      stackClass: 'unpecified',
      stackElement: null as Element | null,
      stackExclude: null as Element[] | null,
      stackMinZIndex: 0,
      isActive: false
    }
  },
  computed: {
    activeZIndex (): number {
      if (typeof window === 'undefined') return 0

      const content = this.stackElement || this.$refs.content
      // Return current zindex if not active

      const index = !this.isActive
        ? getZIndex(content)
        : this.getMaxZIndex(this.stackExclude || [content]) + 2

      if (index == null) return index

      // Return max current z-index (excluding self) + 2
      // (2 to leave room for an overlay below, if needed)
      return parseInt(index)
    }
  },
  methods: {
    getMaxZIndex (exclude: Element[] = []) {
      const base = this.$el
      // Start with lowest allowed z-index or z-index of
      // base component's element, whichever is greater
      const zis = [this.stackMinZIndex, getZIndex(base)]
      // Convert the NodeList to an array to
      // prevent an Edge bug with Symbol.iterator
      // https://github.com/vuetifyjs/vuetify/issues/2146
      const activeElements = [...document.getElementsByClassName(this.stackClass)]

      // Get z-index for all active dialogs
      for (let index = 0; index < activeElements.length; index++) {
        if (!exclude.includes(activeElements[index])) {
          zis.push(getZIndex(activeElements[index]))
        }
      }

      return Math.max(...zis)
    }
  }
})