feat(gtag-plugin): gtag should support multiple tracking ids, notably for the UA => GA4 transition

packages/docusaurus-plugin-google-gtag/src/__tests__/options.test.ts

@@ -0,0 +1,156 @@
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+import {normalizePluginOptions} from '@docusaurus/utils-validation';
+import {
+  validateOptions,
+  type PluginOptions,
+  type Options,
+  DEFAULT_OPTIONS,
+} from '../options';
+import type {Validate} from '@docusaurus/types';
+
+function testValidateOptions(options: Options) {
+  return validateOptions({
+    validate: normalizePluginOptions as Validate<Options, PluginOptions>,
+    options,
+  });
+}
+
+function validationResult(options: Options) {
+  return {
+    id: 'default',
+    ...DEFAULT_OPTIONS,
+    ...options,
+    trackingID:
+      typeof options.trackingID === 'string'
+        ? [options.trackingID]
+        : options.trackingID,
+  };
+}
+
+const MinimalConfig: Options = {
+  trackingID: 'G-XYZ12345',
+};
+
+describe('validateOptions', () => {
+  it('throws for undefined options', () => {
+    expect(
+      // @ts-expect-error: TS should error
+      () => testValidateOptions(undefined),
+    ).toThrowErrorMatchingInlineSnapshot(`""trackingID" is required"`);
+  });
+
+  it('throws for null options', () => {
+    expect(
+      // @ts-expect-error: TS should error
+      () => testValidateOptions(null),
+    ).toThrowErrorMatchingInlineSnapshot(`""value" must be of type object"`);
+  });
+
+  it('throws for empty object options', () => {
+    expect(
+      // @ts-expect-error: TS should error
+      () => testValidateOptions({}),
+    ).toThrowErrorMatchingInlineSnapshot(`""trackingID" is required"`);
+  });
+
+  it('throws for number options', () => {
+    expect(
+      // @ts-expect-error: TS should error
+      () => testValidateOptions(42),
+    ).toThrowErrorMatchingInlineSnapshot(`""value" must be of type object"`);
+  });
+
+  it('throws for null trackingID', () => {
+    expect(
+      // @ts-expect-error: TS should error
+      () => testValidateOptions({trackingID: null}),
+    ).toThrowErrorMatchingInlineSnapshot(
+      `""trackingID" does not match any of the allowed types"`,
+    );
+  });
+  it('throws for number trackingID', () => {
+    expect(
+      // @ts-expect-error: TS should error
+      () => testValidateOptions({trackingID: 42}),
+    ).toThrowErrorMatchingInlineSnapshot(
+      `""trackingID" does not match any of the allowed types"`,
+    );
+  });
+  it('throws for empty trackingID', () => {
+    expect(() =>
+      testValidateOptions({trackingID: ''}),
+    ).toThrowErrorMatchingInlineSnapshot(
+      `""trackingID" does not match any of the allowed types"`,
+    );
+  });
+
+  it('accepts minimal config', () => {
+    expect(testValidateOptions(MinimalConfig)).toEqual(
+      validationResult(MinimalConfig),
+    );
+  });
+
+  it('accepts anonymizeIP', () => {
+    const config: Options = {
+      ...MinimalConfig,
+      anonymizeIP: true,
+    };
+    expect(testValidateOptions(config)).toEqual(validationResult(config));
+  });
+
+  it('accepts single trackingID', () => {
+    const config: Options = {
+      trackingID: 'G-ABCDEF123',
+    };
+    expect(testValidateOptions(config)).toEqual(validationResult(config));
+  });
+
+  it('accepts multiple trackingIDs', () => {
+    const config: Options = {
+      trackingID: ['G-ABCDEF123', 'UA-XYZ456789'],
+    };
+    expect(testValidateOptions(config)).toEqual(validationResult(config));
+  });
+
+  it('throws for empty trackingID arrays', () => {
+    const config: Options = {
+      // @ts-expect-error: TS should error
+      trackingID: [],
+    };
+    expect(() =>
+      testValidateOptions(config),
+    ).toThrowErrorMatchingInlineSnapshot(
+      `""trackingID" does not match any of the allowed types"`,
+    );
+  });
+
+  it('throws for sparse trackingID arrays', () => {
+    const config: Options = {
+      // @ts-expect-error: TS should error
+      trackingID: ['G-ABCDEF123', null, 'UA-XYZ456789'],
+    };
+    expect(() =>
+      testValidateOptions(config),
+    ).toThrowErrorMatchingInlineSnapshot(
+      `""trackingID" does not match any of the allowed types"`,
+    );
+  });
+
+  it('throws for bad trackingID arrays', () => {
+    const config: Options = {
+      // @ts-expect-error: TS should error
+      trackingID: ['G-ABCDEF123', 42],
+    };
+    expect(() =>
+      testValidateOptions(config),
+    ).toThrowErrorMatchingInlineSnapshot(
+      `""trackingID" does not match any of the allowed types"`,
+    );
+  });
+});

packages/docusaurus-plugin-google-gtag/src/index.ts

@@ -5,23 +5,38 @@
  * LICENSE file in the root directory of this source tree.
  */
 
-import {Joi} from '@docusaurus/utils-validation';
-import type {
-  LoadContext,
-  Plugin,
-  OptionValidationContext,
-  ThemeConfig,
-  ThemeConfigValidationContext,
-} from '@docusaurus/types';
+import type {LoadContext, Plugin} from '@docusaurus/types';
 import type {PluginOptions, Options} from './options';
 
+function createConfigSnippet({
+  trackingID,
+  anonymizeIP,
+}: {
+  trackingID: string;
+  anonymizeIP: boolean;
+}): string {
+  return `gtag('config', '${trackingID}', { ${
+    anonymizeIP ? "'anonymize_ip': true" : ''
+  } });`;
+}
+
+function createConfigSnippets({
+  trackingID: trackingIDArray,
+  anonymizeIP,
+}: PluginOptions): string {
+  return trackingIDArray
+    .map((trackingID) => createConfigSnippet({trackingID, anonymizeIP}))
+    .join('\n');
+}
+
 export default function pluginGoogleGtag(
   context: LoadContext,
   options: PluginOptions,
 ): Plugin {
-  const {anonymizeIP, trackingID} = options;
   const isProd = process.env.NODE_ENV === 'production';
 
+  const firstTrackingId = options.trackingID[0];
+
   return {
     name: 'docusaurus-plugin-google-gtag',
 
@@ -60,7 +75,11 @@ export default function pluginGoogleGtag(
             tagName: 'script',
             attributes: {
               async: true,
-              src: `https://www.googletagmanager.com/gtag/js?id=${trackingID}`,
+              // We only include the first tracking id here because google says
+              // we shouldn't install multiple tags/scripts on the same page
+              // Instead we should load one script and use n * gtag("config",id)
+              // See https://developers.google.com/tag-platform/gtagjs/install#add-products
+              src: `https://www.googletagmanager.com/gtag/js?id=${firstTrackingId}`,
             },
           },
           {
@@ -69,37 +88,15 @@ export default function pluginGoogleGtag(
               window.dataLayer = window.dataLayer || [];
               function gtag(){dataLayer.push(arguments);}
               gtag('js', new Date());
-              gtag('config', '${trackingID}', { ${
-              anonymizeIP ? "'anonymize_ip': true" : ''
-            } });`,
+              ${createConfigSnippets(options)};
+              `,
           },
         ],
       };
     },
   };
 }
 
-const pluginOptionsSchema = Joi.object<PluginOptions>({
-  trackingID: Joi.string().required(),
-  anonymizeIP: Joi.boolean().default(false),
-});
-
-export function validateOptions({
-  validate,
-  options,
-}: OptionValidationContext<Options, PluginOptions>): PluginOptions {
-  return validate(pluginOptionsSchema, options);
-}
-
-export function validateThemeConfig({
-  themeConfig,
-}: ThemeConfigValidationContext<ThemeConfig>): ThemeConfig {
-  if ('gtag' in themeConfig) {
-    throw new Error(
-      'The "gtag" field in themeConfig should now be specified as option for plugin-google-gtag. More information at https://github.com/facebook/docusaurus/pull/5832.',
-    );
-  }
-  return themeConfig;
-}
+export {validateThemeConfig, validateOptions} from './options';
 
 export type {PluginOptions, Options};

packages/docusaurus-plugin-google-gtag/src/options.ts

@@ -4,10 +4,58 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  */
+import {Joi} from '@docusaurus/utils-validation';
+import type {
+  OptionValidationContext,
+  ThemeConfig,
+  ThemeConfigValidationContext,
+} from '@docusaurus/types';
 
 export type PluginOptions = {
-  trackingID: string;
+  trackingID: [string, ...string[]];
+  // TODO deprecate anonymizeIP after June 2023
+  // "In Google Analytics 4, IP masking is not necessary
+  // since IP addresses are not logged or stored."
+  // https://support.google.com/analytics/answer/2763052?hl=en
   anonymizeIP: boolean;
 };
 
-export type Options = Partial<PluginOptions>;
+export type Options = {
+  trackingID: string | [string, ...string[]];
+  anonymizeIP?: boolean;
+};
+
+export const DEFAULT_OPTIONS: Partial<PluginOptions> = {
+  anonymizeIP: false,
+};
+
+const pluginOptionsSchema = Joi.object<PluginOptions>({
+  // We normalize trackingID as a string[]
+  trackingID: Joi.alternatives()
+    .try(
+      Joi.alternatives().conditional(Joi.string().required(), {
+        then: Joi.custom((val: boolean) => [val]),
+      }),
+      Joi.array().items(Joi.string().required()),
+    )
+    .required(),
+  anonymizeIP: Joi.boolean().default(DEFAULT_OPTIONS.anonymizeIP),
+});
+
+export function validateOptions({
+  validate,
+  options,
+}: OptionValidationContext<Options, PluginOptions>): PluginOptions {
+  return validate(pluginOptionsSchema, options);
+}
+
+export function validateThemeConfig({
+  themeConfig,
+}: ThemeConfigValidationContext<ThemeConfig>): ThemeConfig {
+  if ('gtag' in themeConfig) {
+    throw new Error(
+      'The "gtag" field in themeConfig should now be specified as option for plugin-google-gtag. More information at https://github.com/facebook/docusaurus/pull/5832.',
+    );
+  }
+  return themeConfig;
+}

packages/docusaurus-plugin-google-gtag/tsconfig.client.json

@@ -10,6 +10,6 @@
     "rootDir": "src",
     "outDir": "lib"
   },
-  "include": ["src/gtag.ts", "src/options.ts", "src/*.d.ts"],
+  "include": ["src/gtag.ts", "src/*.d.ts"],
   "exclude": ["**/__tests__/**"]
 }

website/docs/api/plugins/plugin-google-gtag.mdx

@@ -45,7 +45,7 @@ Accepted fields:
 
 | Name | Type | Default | Description |
 | --- | --- | --- | --- |
-| `trackingID` | `string` | **Required** | The tracking ID of your gtag service. |
+| `trackingID` | <code>string \| string[]</code> | **Required** | The tracking ID of your gtag service. It is possible to provide multiple ids. |
 | `anonymizeIP` | `boolean` | `false` | Whether the IP should be anonymized when sending requests. |
 
 ```mdx-code-block

website/docusaurus.config.js

@@ -357,7 +357,7 @@ const config = {
         },
         gtag: !(isDeployPreview || isBranchDeploy)
           ? {
-              trackingID: 'UA-141789564-1',
+              trackingID: ['G-E5CR2Q1NRE', 'UA-141789564-1'],
             }
           : undefined,
         sitemap: {