createSchema

Creates your own schema from a validation function. Such a schema works everywhere the built-in ones do: in object, pipe, optional — and supports Standard Schema.

Signature

function createSchema<T>(run: (value: unknown, ctx: Ctx, path: Path, parent: unknown) => T | Fail): Schema<T>

function fail(ctx: Ctx, path: Path, code: string, msg?: Message, params?: Record<string, unknown>): Fail
function isEmpty(value: unknown): boolean

Parameters

run parameter	Description
value	The value to validate — can be anything
ctx, path	Pass them to fail on error and to nested schemas
parent	The object containing the value (raw input)

run returns the value (it may be transformed) or the result of fail(...).

• fail(ctx, path, code, msg?, params?) — records an error with code code. The text comes from msg or from the setMessages messages by code; params fill {params}.
• isEmpty(value) — true for undefined, null and '': this is how built-in schemas behave, see Empty values.

Examples

import { createSchema, fail, isEmpty, setMessages, type Message } from 'tinyval';

export const bigint = (msg?: Message) =>
  createSchema<bigint>((value, ctx, path) => {
    if (isEmpty(value)) return fail(ctx, path, 'required', msg);
    if (typeof value !== 'bigint') return fail(ctx, path, 'bigint', msg);
    return value;
  });

setMessages({ bigint: 'Must be a bigint' });

// slug: trims, lowercases and validates
export const slug = (msg?: Message) =>
  createSchema<string>((value, ctx, path) => {
    if (isEmpty(value)) return fail(ctx, path, 'required', msg);
    const s = String(value).trim().toLowerCase();
    return /^[a-z0-9]+(-[a-z0-9]+)*$/.test(s) ? s : fail(ctx, path, 'pattern', msg);
  });

See also

• Custom rules & schemas — when check is enough
• Standard Schema