Function: computedState()

Imported from @react-logic/state

computedState<F>(fn): ComputedReturn<F>

Defined in: state/src/lib/state.ts:218

Plain derivation — call c() to read the latest value.

Input variant — if fn takes one parameter, computedState wraps an internal signal as the input. The returned function is dual-purpose: c() reads the derived value, c(input) writes the input. The signal starts as undefined, so the parameter must accept undefined:

• (q: string | undefined) => … — explicit, handle the undefined case inside the body.
• (q = '') => … — default-arg syntax. The default value is what the callback sees on the first read.

A bare (q: string) => … (no default, no | undefined) is a type error — the runtime would otherwise crash on the first read.

Type Parameters

F

F extends (...args) => unknown

The callback's full signature; the return shape (plain getter vs. getter/setter) is picked off Parameters<F>.

Parameters

fn

F

A function that returns the computed value, optionally from a wrapped input.

Returns

ComputedReturn<F>

Either a getter () => T (zero-param fn) or a dual getter/setter InputComputed<I, T> (one-param fn).

Examples

class Cart {
  items = state<Item[]>([]);
  total = computedState(() => this.items().reduce((s, i) => s + i.price, 0));
}

class Search {
  pattern = computedState((q = '') => new RegExp(q, 'i'));
}
const s = new Search();
s.pattern('foo'); // void — sets the input
s.pattern();      // RegExp(/foo/i)