GA4 Duplicator

Intercepts Google Analytics 4 (GA4) collect requests and duplicates them to a D8A server endpoint.

What it does

This library provides browser-based network interception to duplicate GA4 analytics calls. It intercepts requests made to Google Analytics and forwards them to a configured D8A server endpoint, enabling parallel data collection.

Supported interception methods:

• Fetch API requests
• XMLHttpRequest calls
• navigator.sendBeacon calls
• Script tag loads

Usage

Include the built script in your HTML and initialize the duplicator:

<script src="dist/gd.min.js"></script>
<script>
  window.createGA4Duplicator({
    server_container_url: "https://your-d8a-endpoint.com",
    debug: false
  });
</script>

Configuration Options

• server_container_url: Default D8A server endpoint URL. Can be overridden for each destination.
• destinations: Array of destination objects with measurement_id, server_container_url, and optional convert_to_get (default: []).
• debug: Enable debug logging (default: false).
• convert_to_get: Convert POST requests into multiple GET requests (default: false). This is useful for environments that don't support POST or when you want to split batched requests into individual hits.

Multiple Destinations

window.createGA4Duplicator({
  server_container_url: "https://default-endpoint.com",
  destinations: [
    {
      measurement_id: "G-ABC123",
      server_container_url: "https://endpoint1.com",
    },
    {
      measurement_id: "G-XYZ789",
      server_container_url: "https://endpoint2.com",
      convert_to_get: true
    }
  ]
});

Build

Production build (minified):

npm run build:prod

Output: dist/gd.min.js

Development build:

npm run build:dev

Output: dist/gd.js

Source Code Hashing

The build process generates a SHA256 hash of all TypeScript source files in the src/ directory and saves it to src.hash. This ensures build integrity and enables CI verification.

Verify source code integrity:

npm run hash

This command compares the stored hash with the current source code hash:

• Exit code 0: Source code matches the hash (build is up-to-date)
• Exit code 1: Source code has changed since last build

Use this in CI pipelines to ensure dist/ files are regenerated when source code changes.

Test

Unit tests:

npm test

End-to-end tests:

1. Install Playwright browsers (first time only):

npx playwright install chromium

2. Run e2e tests:

npm run test:e2e

The e2e tests start a local HTTP server and use Playwright to verify that GA4 requests are properly duplicated to the D8A endpoint.

Manual testing:

Open test.html in a browser to manually test different network interception methods. The page includes buttons to trigger various types of GA4 requests and displays logs of duplication activity.