Hello.

My QRCode scanner app in China ran into an issue offline: the camera wouldn't start due to a Google Analytics request hanging in the onload event. This highlighted a broader problem of render-blocking third-party assets. If these assets (like scripts) are critical, a slow or failed connection can prevent the page from rendering for over a minute while the browser waits for a timeout. This results in a blank screen for the user. This post explores the impact of render-blocking third-party resources on performance and how optimizing their integration can drastically improve the user experience, particularly in unreliable network conditions.

In this post, I share how I used Comlink to simplify the worker logic in my QRSnapper project, which aims to achieve 60fps UI and near-instant QR code detection using getUserMedia. The code now utilizes the Barcode Detection API within a Web Worker for efficient QR code scanning. If the native API is available, the code uses it; otherwise, it falls back to a polyfill. This approach keeps the UI responsive while offloading the processing to a separate thread, significantly improving performance.

The fastest QR Code scanner on the web