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:

``html


`

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- server_container_url: Default D8A server endpoint URL.Can be overridden for each destination.
- destinations: Array of destination objects with measurement_id and server_container_url (default: []).
- debug: Enable debug logging (default: false)

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`javascript
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"
}
]
});
`

Build

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`bash
npm run build:prod
`
Output: dist/gd.min.js

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`bash
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.

$3


`bash
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

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`bash
npm test
`

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1. Install Playwright browsers (first time only):
`bash
npx playwright install chromium
`

2. Run e2e tests:
`bash
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.

$3

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.