Frontend

在iOS上查询排版结果只需一行代码，Web上需要触发整个页面的重新布局。这不是因为浏览器工程师蠢，而是CSS在1994年做了一个声明式的架构选择。这个选择的天花板更高，但代价是中间状态不可查询。Facebook在2012年因为不理解这个trade-off付出了数亿美元的代价。SwiftUI和Jetpack Compose证明了声明式和可观测可以共存，关键在于分层。这个教训适用于所有系统设计：好的抽象让你选择在哪一层工作，坏的抽象把所有层粘在一起让你没得选。

Querying layout results takes one line of code on iOS, Android, Qt, and Flutter. On the web, it requires triggering a full-page reflow. This isn't because browser engineers are incompetent. CSS made a deliberate architectural choice in 1994 toward declarative layout, which has a higher ceiling but hides intermediate state. Facebook paid hundreds of millions of dollars in 2012 for not understanding this trade-off. SwiftUI and Jetpack Compose prove that declarative and observable can coexist through proper layering. The lesson applies to all system design: good abstractions let you choose which layer to work at; bad abstractions glue all layers together and leave you no choice.