version: "1.0.0" name: tsentials-validation description: Use when validating a model with fluent, eager, Result-based rules — Validator.validate with rules.for('path').notEmpty().maxLength(), nested paths and forEach for collections, cascade modes, subclassable Validator<T>, validateAsync with mustAsync and AbortSignal, validateWith as a railway step.

tsentials/validation

Fluent model validation that returns Result<T>. Rules run eagerly; the success value is the validated instance. Subpath-only: not exported from the root tsentials entry.

Installation

npm install tsentials

Import

import { Validator, CascadeMode } from 'tsentials/validation';
import type { RuleContext, RuleChain, Configure, AsyncConfigure } from 'tsentials/validation';

Inline validation

type User = { name: string; email: string; address: { city: string }; items: { sku: string }[] };
const r = Validator.validate(user, (rules) => {
  rules.for('name').notEmpty().maxLength(50);
  rules.for('email').notEmpty().emailAddress();
  rules.for('address.city').notEmpty();            // dotted paths are type-checked
  rules.forEach('items', (item) => {
    item.for('sku').notEmpty();
  });
});
// r: Result<User>
// failure codes: 'name.NotEmpty', 'email.EmailAddress', 'address.city.NotEmpty', 'items[0].sku.NotEmpty'

Error code format is <path>.<Rule>; all errors have type Validation.

Validator subclass

class UserValidator extends Validator<User> {
  protected configure(rules: RuleContext<User>) {
    rules.for('name').notEmpty().cascade(CascadeMode.Continue).minLength(3).maxLength(50);
  }
}
const validator = new UserValidator();
validator.validate(user);        // Result<User>
validator.toRule();              // Rule<User> — plug into RuleEngine (tsentials/rules)

Cascade and null handling

• Default cascade is Stop: the first failure on a chain skips the remaining rules of that chain. Use .cascade(CascadeMode.Continue) to accumulate.
• null/undefined are skipped by every built-in rule except notNull, notEmpty and equal. Guard optional values with notEmpty() first.

Built-in rules (on rules.for(...))

rules.forEach(path, configure) validates each element; rules.self() validates the model itself; rules.addFailure(code, description) adds an error directly.

Async validation

const r = await Validator.validateAsync(
  user,
  async (rules, _model, signal) => {
    await rules.for('email').mustAsync(async (e) => await isFree(e, signal), 'Email.Taken', 'Already used');
  },
  { signal },
);

Await every async rule (mustAsync, forEachAsync, setValidatorAsync, satisfiesAsync) inside the callback. validate() throws TypeError if configure returns a promise or leaves an async rule un-awaited.

Railway step

import { Result } from 'tsentials/result';
const checked = Validator.validateWith(Result.success(user), (rules) => {
  rules.for('name').notEmpty();
});
// failure input passes through unchanged; also: Validator.validateWithAsync

Patterns and pitfalls

• Import from tsentials/validation — never from the root tsentials entry.
• AbortSignal convention: the caller's abort makes the promise reject with signal.reason; it never becomes a validation error. An exception thrown by an async rule predicate or by configure rejects too (never a failure); use mustAsync predicates that return false for validation failures.
• Subclasses implement configure(rules) as a sync method; use validateAsync with an AsyncConfigure for async rules.
• Errors use description, not message: r.errors[0]?.description.
• A message argument may be a string or an AppError.