Validation

Validation

The validation module provides stateless, rule-based input validation. It works with any plain object — form data, JSON bodies, URL params — and returns a typed result you can inspect without throwing exceptions.

Import

import { validate, defineRules } from '@loewen-digital/fullstack/validation'

Basic usage

import { validate } from '@loewen-digital/fullstack/validation'

const result = validate(
  { email: 'alice@example.com', password: 'secret123' },
  {
    email: ['required', 'email'],
    password: ['required', 'min:8'],
  }
)

if (!result.passes) {
  console.log(result.errors)
  // { password: ['The password must be at least 8 characters.'] }
}

// result.data is the validated (and trimmed) input
console.log(result.data.email) // 'alice@example.com'

Working with FormData

const formData = await request.formData()

const result = validate(Object.fromEntries(formData), {
  username: ['required', 'string', 'min:3', 'max:32'],
  email: ['required', 'email'],
  age: ['required', 'numeric', 'min:18'],
})

Available rules

Rule	Description
required	Field must be present and non-empty
string	Must be a string
numeric	Must be a number or numeric string
boolean	Must be a boolean-like value
email	Must be a valid email address
url	Must be a valid URL
min:n	Minimum length (strings) or value (numbers)
max:n	Maximum length (strings) or value (numbers)
between:min,max	Value must be between min and max
in:a,b,c	Value must be one of the listed options
not_in:a,b,c	Value must not be one of the listed options
regex:/pattern/	Must match the given regular expression
confirmed	Field must have a matching _confirmation field
nullable	Field may be null or absent
array	Must be an array
date	Must be a parseable date string

Custom rules

import { defineRules, validate } from '@loewen-digital/fullstack/validation'

const rules = defineRules({
  slug: (value) => {
    if (!/^[a-z0-9-]+$/.test(String(value))) {
      return 'The :attribute may only contain lowercase letters, numbers, and hyphens.'
    }
  },
})

const result = validate({ slug: 'Hello World' }, { slug: ['required', 'slug'] }, { rules })

Config options

validate() accepts an optional third argument:

Option	Type	Default	Description
rules	Record<string, RuleFn>	{}	Custom rule definitions
messages	Record<string, string>	{}	Custom error message overrides
bail	boolean	false	Stop after the first failure per field