feat: add google analytics gtag.js plugin

build/build.js

@@ -80,6 +80,7 @@ async function buildAllPlugin() {
   var plugins = [
     {name: 'search', input: 'search/index.js'},
     {name: 'ga', input: 'ga.js'},
+    {name: 'gtag', input: 'gtag.js'},
     {name: 'matomo', input: 'matomo.js'},
     {name: 'emoji', input: 'emoji.js'},
     {name: 'external-script', input: 'external-script.js'},

docs/plugins.md

@@ -89,6 +89,28 @@ Configure by `data-ga`.
 <script src="//cdn.jsdelivr.net/npm/docsify/lib/plugins/ga.min.js"></script>
 ```
 
+## Google Universal Analytics (gtag.js)
+
+Usage is same as `Google Analytics`.
+
+```html
+<script>
+  window.$docsify = {
+    ga: 'UA-XXXXX-Y'
+  }
+</script>
+<script src="//cdn.jsdelivr.net/npm/docsify/lib/docsify.min.js"></script>
+<script src="//cdn.jsdelivr.net/npm/docsify/lib/plugins/gtag.min.js"></script>
+```
+
+Configure by `data-ga`.
+
+```html
+<script src="//cdn.jsdelivr.net/npm/docsify/lib/docsify.min.js" data-ga="UA-XXXXX-Y"></script>
+<script src="//cdn.jsdelivr.net/npm/docsify/lib/plugins/gtag.min.js"></script>
+```
+
+
 ## emoji
 
 The default is to support parsing emoji. For example `:100:` will be parsed to :100:. But it is not precise because there is no matching non-emoji string. If you need to correctly parse the emoji string, you need install this plugin.

src/plugins/gtag.js

@@ -0,0 +1,47 @@
+/* eslint-disable no-console */
+// copy from ./ga.js
+// usage is the same as ./ga.js
+function appendScript(id) {
+  const script = document.createElement('script');
+  script.async = true;
+  script.src = 'https://www.googletagmanager.com/gtag/js?id=' + id;
+  document.body.appendChild(script);
+}
+
+function init(id) {
+  appendScript(id);
+
+  window.dataLayer = window.dataLayer || [];
+  window.gtag =
+    window.gtag ||
+    function() {
+      window.dataLayer.push(arguments);
+    };
+
+  window.gtag('js', new Date());
+  window.gtag('config', id);
+}
+
+function collect() {
+  if (!window.ga) {
+    init($docsify.ga);
+  }
+
+  // usage: https://developers.google.com/analytics/devguides/collection/gtagjs/pages
+  window.gtag('event', 'page_view', {
+    page_title: document.title,
+    page_location: location.href,
+    page_path: location.pathname,
+  });
+}
+
+const install = function(hook) {
+  if (!$docsify.ga) {
+    console.error('[Docsify] ga is required.');
+    return;
+  }
+
+  hook.beforeEach(collect);
+};
+
+$docsify.plugins = [].concat(install, $docsify.plugins);