Computed

Create a computed

const count = new Signal(2);
const double = new Computed(() => count.value * 2);
const label = computed(() => `${count.value} items`);

double.value; // 4

A computed reads like a signal but you cannot write it. It recomputes lazily: only when it is read after a signal it depends on changed.

Like a signal, double.peek() reads the current value without tracking it.

Example

Chains

Computed values can read other computed values. Each one recomputes at most once per change, however many readers it has.

const items = new Signal([3, 8, 1]);
const sorted = computed(() => [...items.value].sort((a, b) => a - b));
const smallest = computed(() => sorted.value[0]);