Function signal

Creates a reactive signal that can hold and notify changes to a value.

Signals are the fundamental reactive primitive. They store a value and notify subscribers when the value changes. Reading a signal automatically tracks dependencies when inside an effect or computed.

Isomorphic: Works identically across all JavaScript runtimes. Performance: Optimized for frequent reads and infrequent writes. Memory: Automatic cleanup when all subscribers are removed.

// Create signal
const count = signal(0);

// Read value (tracks dependency if in effect/computed)
console.log(count()); // 0

// Update value
count.set(5);
count.update(n => n + 1); // 6

// Read without tracking
console.log(count.peek()); // 6

// Subscribe to changes
const unsub = count.subscribe(value => console.log('New:', value));
count.set(10); // Logs: "New: 10"
unsub(); // Clean up
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// Isomorphic usage - same code everywhere
const data = signal(null);

// Works in Node.js
if (typeof process !== 'undefined') {
  data.set({ platform: 'node' });
}

// Works in browser
if (typeof window !== 'undefined') {
  data.set({ platform: 'browser' });
}

// Works in Deno/Bun
data.set({ platform: 'universal' });
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