Preact Signals provide a minimal signal implementation that works with Preact or React:

const count = signal(0); const doubled = computed(() => count.value * 2);

Signals break component boundaries. A signal defined in one component can be read by any other component that imports it. This enables powerful patterns but violates React's principle that data flows down through props and up through callbacks.

The convergence on signals across frameworks proves the pattern's universality. Each framework adapted signals to its existing architecture while preserving the core mental model.

Signals libraries for React: @preact/signals-react and jotai provide signal-like primitives that work within React's model. These are viable for performance-critical components.

The convergence of major frameworks on signals-based reactivity is not fashion—it is a recognition that the virtual DOM model, while powerful, has a fundamental inefficiency: it describes what to render rather than what changed. Signals describe exactly what changed and update exactly what depends on it.

Signal-native adapters implement it with their framework primitives and can keep option reads in the same reactive graph.

Signals invert this. Instead of "re-run everything and figure out what changed," signals say "run only what is directly subscribed to the specific value that changed." The computational difference is significant in applications with large component trees and frequent state updates.