It&#x27;s not so much Javascript itself that is the issue so much as the reliance on HTML&#x2F;CSS for the UI. iOS (and recent versions of Android) are designed around the performance limitations of their devices (especially on early hardware), and there are a lot of optimizations in their respective UI frameworks to ensure the UI stays responsive, and scrolling stays smooth, even when working with large amounts of data.<p>Throwing the kitchen sink at developers in the form of HTML&#x2F;CSS does not encourage performant design, and indeed when you read stories of developers trying to write complex mobile apps using web technologies it often eventually devolves into a performance optimization game (that doesn&#x27;t always succeed).<p>That said, I&#x27;m sure someone could put together a UI framework based on JS that rivals the perormance of iOS or Android. But no one has bothered to do so because they view HTML&#x2F;CSS as &quot;good enough&quot;. Which is critically flawed thinking.