vuepress: @vuepress/google-analytics does not add tracking code as window is undefined?

• I confirm that this is a issue rather than a question.

Bug report

if I am building via vuepress build docs but window is undefined. not really suprising as it does not run in the browser? However there is this check

export default ({ router }) => {
  console.log(typeof window);  // undefined
  // Google analytics integration
  if (process.env.NODE_ENV === 'production' && GA_ID && typeof window !== 'undefined') {

from this change a while back: https://github.com/vuejs/vuepress/pull/893/commits/ca618e4b6c1cf5857f90f7d41848668ae56e3aa3

I’m still not sure why a check for window is there?

Version

every version? I know it worked before so I’m baffled how?

tested in:

$ npm ls vuepress
@open-wc/root@ [...]/open-wc/open-wc
└── vuepress@1.0.0-alpha.37

$ npm ls @vuepress/plugin-google-analytics
@open-wc/root@ [...]/open-wc/open-wc
└── @vuepress/plugin-google-analytics@1.0.0-alpha.37

Steps to reproduce

add to your config.js

  plugins: [
    '@vuepress/google-analytics',
    {
      'ga': 'UA-131782693-1'
    }
  ],

live version:

git clone git@github.com:open-wc/open-wc.git
cd open-wc
npm i
npm run site:build
// search for "google-analytics" in the "_site" folder

What is expected?

tracking via analytics e.g. js tracking code get’s inserted

What is actually happening?

no tracking code

Other relevant information

$ node --version
v11.7.0

$ npm --version
6.6.0

$ cat /proc/version:
It is a WSL (Windows Subystem Linux)
Linux version 4.4.0-17134-Microsoft (Microsoft@Microsoft.com) (gcc version 5.4.0 (GCC) ) #523-Microsoft Mon Dec 31 17:49:00 PST 2018

$ lsb_release -a:
Distributor ID: Ubuntu
Description:    Ubuntu 16.04.3 LTS
Release:        16.04
Codename:       xenial

• Is this a global or local install? local
• Which package manager did you use for the install? yarn or npm didn’t matter