withSchema()

Wraps a store with runtime schema validation. Invalid upstream values are rejected (not forwarded) and the error is exposed via an error companion store.

Signature

function withSchema<T>(
	store: Store<unknown>,
	schema: Schema<T>,
	opts?: WithSchemaOptions,
): WithSchemaStore<T>

Parameters

Parameter	Type	Description
store	Store<unknown>	The source store to validate.
schema	Schema<T>	Any object with parse(v: unknown): T. Throws on invalid input.
opts	WithSchemaOptions	Optional configuration.

Returns

WithSchemaStore<T> — a store that only emits valid values, with error companion and set() for validated writes.

Basic Usage

import { state, subscribe } from 'callbag-recharge';
import { withSchema } from 'callbag-recharge/utils';

const raw = state<unknown>(0);
const validated = withSchema(raw, { parse: (v) => { if (typeof v !== 'number') throw new Error('not a number'); return v; } });
subscribe(validated.error, e => console.log(e?.message)); // "not a number"
raw.set("bad"); // rejected — error companion fires
raw.set(42);    // passes — emitted downstream, error cleared

Options / Behavior Details

• Schema interface: { parse(v: unknown): T } — compatible with Zod (z.string()), Valibot (v.string()), ArkType, or any custom validator that throws on invalid input.
• Rejection: Invalid values are silently dropped (not forwarded downstream). The error companion store is set with the validation error.
• Writable: If the input store has set(), the returned store's set() validates before forwarding. Invalid values are rejected with error set. Throws if upstream is read-only.
• Initial validation: Throws at construction if the store's initial value fails schema validation. This ensures get() always returns a valid T.