docsify/src/plugins/ga.js

// From https://github.com/egoist/vue-ga/blob/master/src/index.js

function appendScript () {
  const script = document.createElement('script')
  script.async = true
  script.src = 'https://www.google-analytics.com/analytics.js'
  document.body.appendChild(script)
}

function init (id) {
  if (!window.ga) {
    appendScript()
    window.ga = window.ga || function () {
      (window.ga.q = window.ga.q || []).push(arguments)
    }
    window.ga.l = Number(new Date())
    window.ga('create', id, 'auto')
  }
}

function collect () {
  init(window.$docsify.ga)
  window.ga('set', 'page', location.href)
  window.ga('send', 'pageview')
}

const install = function () {
  if (install.installed) return
  install.installed = true

  if (!window.$docsify.ga) {
    console.error('[Docsify] ga is required.')
    return
  }

  window.$docsify.plugins = [].concat(function (hook) {
    hook.init(collect)
    hook.beforeEach(collect)
  }, window.$docsify.plugins)
}

export default install()