Merge branch 'develop' into es-modules

src/plugins/gtag.js

@@ -0,0 +1,72 @@
+/* eslint-disable no-console */
+// From ./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);
+}
+
+// global site tag instance initialized
+function initGlobalSiteTag(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);
+}
+
+// add additional products to your tag
+// https://developers.google.com/tag-platform/gtagjs/install
+function initAdditionalTag(id) {
+  window.gtag('config', id);
+}
+
+function init(ids) {
+  if (Array.isArray(ids)) {
+    // set the first id to be a global site tag
+    initGlobalSiteTag(ids[0]);
+
+    // the rest ids
+    ids.forEach((id, index) => {
+      if (index > 0) {
+        initAdditionalTag(id);
+      }
+    });
+  } else {
+    initGlobalSiteTag(ids);
+  }
+}
+
+function collect() {
+  if (!window.gtag) {
+    init($docsify.gtag);
+  }
+
+  // usage: https://developers.google.com/analytics/devguides/collection/gtagjs/pages
+  window.gtag('event', 'page_view', {
+    /* eslint-disable camelcase */
+    page_title: document.title,
+    page_location: location.href,
+    page_path: location.pathname,
+    /* eslint-disable camelcase */
+  });
+}
+
+const install = function (hook) {
+  if (!$docsify.gtag) {
+    console.error('[Docsify] gtag is required.');
+    return;
+  }
+
+  hook.beforeEach(collect);
+};
+
+$docsify.plugins = [].concat(install, $docsify.plugins);