How Partytown Offloads Third-Party Scripts to Fix Google's INP Metric

Since March 12, 2024, Google replaced First Input Delay with Interaction to Next Paint (INP) as a Core Web Vital, measuring the time between any user interaction and the browser's next painted frame. A key cause of poor INP scores is third-party scripts — such as tag managers, analytics pixels, and A/B testing tools — that block the browser's single main thread and delay responses to user input. Partytown, a lightweight library maintained by the QwikDev team, addresses this by moving third-party scripts off the main thread and into a web worker, communicating with the DOM through a proxy. This approach frees the main thread for an application's own code, reducing input delay and improving responsiveness scores. The library can be integrated into frameworks like React and Angular, though it is not suitable for all use cases.