Developed a scalable web application that allows users to upload large Excel files with over 1M rows, with data processing handled entirely client-side to optimize performance. Shifted key logic from memory to IndexedDB, reducing RAM usage from 4GB to 100MB for datasets of 300K rows. Implemented dynamic pagination and ensured refresh-proof functionality for a smooth user experience. This architecture enabled users to securely filter and send data for confidential processing without backend storage.