Complete Reference — Form Validation

All Built-In Rules at a Glance

Rule	Companion Message Property	Control Types
`required: true`	`requiredMessage`	All
`minLength: n`	`minLengthMessage`	text, textarea, password, url
`maxLength: n`	`maxLengthMessage`	text, textarea, password, url
`min: n`	`minMessage`	number
`max: n`	`maxMessage`	number
`email: true`	`emailMessage`	email, text
`url: true`	`urlMessage`	url, text
`pattern: "regex"`	`patternMessage`	text, textarea, email
`minDate: "date"`	`minDateMessage`	date, datetime
`maxDate: "date"`	`maxDateMessage`	date, datetime
`matchesField: "id"`	`matchesFieldMessage`	text, password, email
`minSelections: n`	`minSelectionsMessage`	multiselect
`maxSelections: n`	`maxSelectionsMessage`	multiselect
`minRows: n`	`minRowsMessage`	data-table
`maxRows: n`	`maxRowsMessage`	data-table
`fileTypes: [...]`	`fileTypesMessage`	file-upload
`maxFileSizeMb: n`	`maxFileSizeMbMessage`	file-upload
`requiredWhen: "expr"`	`requiredMessage`	All
`validateWhen: "expr"`	—	All
`revalidateOnChange: [...]`	—	All

ValidationEngine API

import { ValidationEngine } from '@atlas-forms/validation-js';

const engine = new ValidationEngine();

// Validate a single field
const result = await engine.validateField(
  fieldId: string,
  value: any,
  validationConfig: ValidationConfig,
  allValues: Record<string, any>
);

// Validate all fields in the form
const results = await engine.validateAll(
  controls: FormControl[],
  values: Record<string, any>
);
// Returns: Record<string, ValidationResult>

// Check if the form is valid
const isValid = engine.isFormValid(results);

// Get all error messages
const errors = engine.getErrors(results);
// Returns: Array<{ fieldId: string; message: string }>

Common Validation Patterns

Registration Form

[
  {
    "id": "username",
    "type": "text",
    "label": "Username",
    "validation": {
      "required": true,
      "minLength": 3, "maxLength": 30,
      "pattern": "^[a-zA-Z0-9_\\-]+$",
      "customRule": { "name": "usernameAvailable", "async": true,
                      "message": "Username is already taken" }
    }
  },
  {
    "id": "email",
    "type": "email",
    "label": "Email Address",
    "validation": {
      "required": true, "email": true,
      "customRule": { "name": "emailAvailable", "async": true,
                      "message": "An account with this email already exists" }
    }
  },
  {
    "id": "password",
    "type": "password",
    "label": "Password",
    "validation": { "required": true, "minLength": 12 }
  },
  {
    "id": "confirm-password",
    "type": "password",
    "label": "Confirm Password",
    "validation": {
      "required": true,
      "matchesField": "password",
      "matchesFieldMessage": "Passwords do not match",
      "revalidateOnChange": ["password"]
    }
  }
]

Troubleshooting Guide

Problem	Cause	Fix
Validator not found error	Validator name not registered before form renders	Call `registerAllValidators()` before `ReactDOM.render()`
Cross-field rule not re-running	Missing `revalidateOnChange` on dependent field	Add `"revalidateOnChange": ["source-field-id"]`
Async validator runs on every keystroke	`autoValidate: true` without debounce in validator	The engine debounces automatically; if still flooding, check if validator is marked `async: true`
Required rule fires on hidden field	Field is hidden by `visibilityRule` but still validated	Add matching `validateWhen` expression to skip validation when hidden
Error message not appearing	Field not touched and `validateOn: "blur"`	Use `autoValidate: true` or click another field to trigger blur validation
Inline expression validator always passes	Expression syntax error — returns `undefined` (truthy)	Test expression in browser console with `eval()`; check `value` and `allValues` variable names

← Security Validation

Complete Validation Reference

All Built-In Rules at a Glance

ValidationEngine API

Common Validation Patterns

Registration Form

Troubleshooting Guide