vue-devtools/packages/app-backend-core/src/legacy/scan.ts

import { isBrowser, target } from '@vue-devtools/shared-utils'
import { getPageConfig } from '../page-config'

const rootInstances = []

/**
 * Scan the page for root level Vue instances.
 */
export function scan() {
  rootInstances.length = 0

  let inFragment = false
  let currentFragment = null

  function processInstance(instance) {
    if (instance) {
      if (!rootInstances.includes(instance.$root)) {
        instance = instance.$root
      }
      if (instance._isFragment) {
        inFragment = true
        currentFragment = instance
      }

      // respect Vue.config.devtools option
      let baseVue = instance.constructor
      while (baseVue.super) {
        baseVue = baseVue.super
      }
      if (baseVue.config && baseVue.config.devtools) {
        rootInstances.push(instance)
      }

      return true
    }
  }

  if (isBrowser) {
    const walkDocument = (document) => {
      walk(document, (node) => {
        if (inFragment) {
          if (node === currentFragment._fragmentEnd) {
            inFragment = false
            currentFragment = null
          }
          return true
        }
        const instance = node.__vue__

        return processInstance(instance)
      })
    }
    walkDocument(document)

    const iframes = document.querySelectorAll<HTMLIFrameElement>('iframe')
    for (const iframe of iframes) {
      try {
        walkDocument(iframe.contentDocument)
      }
      catch (e) {
        // Ignore
      }
    }

    // Scan for Vue instances in the customTarget elements
    const { customVue2ScanSelector } = getPageConfig()
    const customTargets = customVue2ScanSelector ? document.querySelectorAll(customVue2ScanSelector) : []
    for (const customTarget of customTargets) {
      try {
        walkDocument(customTarget)
      }
      catch (e) {
        // Ignore
      }
    }
  }
  else {
    if (Array.isArray(target.__VUE_ROOT_INSTANCES__)) {
      target.__VUE_ROOT_INSTANCES__.map(processInstance)
    }
  }

  return rootInstances
}

/**
 * DOM walk helper
 *
 * @param {NodeList} nodes
 * @param {Function} fn
 */

function walk(node, fn) {
  if (node.childNodes) {
    for (let i = 0, l = node.childNodes.length; i < l; i++) {
      const child = node.childNodes[i]
      const stop = fn(child)
      if (!stop) {
        walk(child, fn)
      }
    }
  }

  // also walk shadow DOM
  if (node.shadowRoot) {
    walk(node.shadowRoot, fn)
  }
}