UI engineering — the decisions between the design and the framework

There is a layer that neither the design skill nor the framework skill owns. The design says what the screen should be. The framework says how its API works. In between sits every decision that makes an interface either durable or a maintenance tax — and it is where most interface work actually goes wrong.

Nothing here is framework-specific. These decisions are the same in React, Vue, Svelte, SwiftUI and plain HTML; only the syntax moves.

The one rule

State goes to the outermost place that still needs it, and no further. Almost every interface tangle is that rule broken in one of two directions: state hoarded in a component that others need, or state hoisted into a global store that only one component ever reads.