How I Built a Client-Side Engine to Process 75,000 Excel Rows in the Browser (Without Crashing)

When building B2B SaaS tools, there is a dirty little secret in the industry: most "file processing" utilities are a data privacy nightmare. I recently launched Bulk Barcode Generator , an enterprise tool that allows logistics managers to convert .xlsx or .csv shipping manifests into print-ready thermal barcode labels (Code-128, EAN-13, etc.). When I analyzed my legacy competitors, I noticed they all did the same thing: User uploads a sensitive corporate spreadsheet. The file is sent via POST re