Zod

const stringLengthSchema = z.string().transform(v => v.length);
const parsedLengthRes = stringLengthSchema.safeParse('abc'); // { success: true, data: 3 }, { success: false, error }

const UserSchema = z.object({
  name: z.string().trim().min(1),
  age: z.number().optional()
});
const userA = UserSchema.parse({ name: 'a' });
type User = z.infer<typeof UserSchema>;