Validation Overview

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

Basic Usage

Define validation in validation:

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

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

Validator	Description	Error Key
required(path.field)	Field must have value	required
email(path.field)	Valid email format	email
minLength(path.field, n)	Minimum string length	minLength
maxLength(path.field, n)	Maximum string length	maxLength
min(path.field, n)	Minimum number value	min
max(path.field, n)	Maximum number value	max
pattern(path.field, regex)	Match regex pattern	pattern
url(path.field)	Valid URL format	url
phone(path.field)	Valid phone format	phone
number(path.field)	Must be a number	number
date(path.field)	Valid date	date

Conditional Validation

Apply validation only when condition is met:

import { when } from '@reformer/core/validators';

validation: (path) => {
  when(
    () => form.controls.contactByPhone.value === true,
    (path) => {
      required(path.phone);
    }
  );
};

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