checkAsync

A custom async check: a database query, an external API. Works only with validateAsync and parseAsync.

Signature

function checkAsync<T>(fn: (value: T, info: Info) => Promise<boolean> | boolean, msg?: Message): Action<T>

Parameters

Parameter	Type	Description
fn	(value: T, info: Info) => Promise<boolean> | boolean	The check. info — as in check
msg	Message	Custom error message. A string with {params} or a function

Error codes

Code	When	Default message
invalid	fn returned false	Invalid value

You can change the texts: see Messages & i18n.

Notes

• Runs after all synchronous rules of the field and only if they passed — an invalid email never reaches the database.
• Async checks of different fields run in parallel.
• validate and parse throw for such a schema — use the async version.
• It doesn't change the value: checkAsync only checks.

Example

Unique email

const Signup = object({
  email: pipe(
    string(),
    trim(),
    toLowerCase(),
    email(),
    checkAsync(async (v) => !(await db.users.exists({ email: v })), 'Email is already registered'),
  ),
});

const result = await validateAsync(Signup, req.body);

See also

• validateAsync
• parseAsync
• check — sync version