Subito cuts React dropdown load time from 1,256ms to 96ms using virtualization

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Subito's engineering team identified a severe performance bottleneck in their marketplace's Brand filter dropdown, which listed around 1,175 options. On mobile devices with throttled CPUs, opening the dropdown triggered an Interaction to Next Paint (INP) score of 1,256ms — well below Google's 200ms threshold for a 'good' rating. The root cause was React simultaneously mounting over 1,175 component instances the moment the menu opened, creating a large synchronous rendering block. The team resolved this by implementing list virtualization, a technique that renders only the rows currently visible on screen rather than the entire dataset. This targeted fix brought the INP down to 96ms without requiring a full rewrite or heavy third-party libraries.

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