Validation Overview

ReFormer provides declarative validation with built-in validators and support for custom validation.

Basic Usage

Define validation in validation. ReFormer separates operators (validate, validateAsync, validateGroup, applyWhen, apply, validateItems) that register validators in the schema from validator factories (required, email, min, …) that return pure Validator<TForm, TField> functions of shape (value, control, root) => ValidationError | null.

import { GroupNode } from '@reformer/core';
import { validate, required, email, minLength } from '@reformer/core/validators';

const form = new GroupNode({
  form: {
    name: { value: '' },
    email: { value: '' },
  },
  validation: (path) => {
    validate(path.name, required());
    validate(path.name, minLength(2));
    validate(path.email, required());
    validate(path.email, email());
  },
});

Validation State

// Check validation state
form.valid; // true if all fields valid
form.invalid; // true if any field invalid

// Check specific field
form.controls.name.valid;
form.controls.name.errors; // { required: true } or null

Error Messages

Access errors on individual fields:

const name = form.controls.name;

name.errors;
// null - when valid
// { required: true } - when required fails
// { minLength: { required: 2, actual: 1 } } - when minLength fails

Built-in Validator Factories

All factories return a Validator<TForm, TField>. Pass them to validate().

Factory	Used as	Error Key
required()	validate(path.field, required())	required
email()	validate(path.field, email())	email
minLength(n)	validate(path.field, minLength(n))	minLength
maxLength(n)	validate(path.field, maxLength(n))	maxLength
min(n)	validate(path.field, min(n))	min
max(n)	validate(path.field, max(n))	max
pattern(regex)	validate(path.field, pattern(regex))	pattern
url()	validate(path.field, url())	url
phone()	validate(path.field, phone())	phone
isNumber()	validate(path.field, isNumber())	isNumber
integer()	validate(path.field, integer())	integer
multipleOf(n)	validate(path.field, multipleOf(n))	multipleOf
nonNegative()	validate(path.field, nonNegative())	nonNegative
nonZero()	validate(path.field, nonZero())	nonZero
isDate()	validate(path.field, isDate())	date_invalid
notEmpty()	validate(path.array, notEmpty())	minLength

Conditional Validation

Apply validation only when condition is met:

import { applyWhen, validate, required } from '@reformer/core/validators';

validation: (path) => {
  applyWhen(
    path.contactByPhone,
    (value) => value === true,
    (path) => {
      validate(path.phone, required());
    }
  );
};

Validation Timing

Validation runs automatically when:

• Value changes
• Field is touched (for display purposes)

// Manual validation
form.validate(); // Validate entire form

Next Steps

• Built-in Validators — All validators with examples
• Async Validation — Server-side validation
• Custom Validators — Create your own validators