A tiny, but fast and reliable validation library for forms and runtime datatype checks

Form validation can become a complex thing to implement. The idea of this library is to take a straight-forward, functional approach to the API, allow for composition, but at the same time provide all the primitives necessary to do the most relevant validations such as email etc. out-of-the-box.

Also, usually, form validation and runtime datatype checking are thought of as two pairs of shoes, which leads to code duplication because logically, most form validation libraries need to use a foundation of runtime datatype checks. In this library, all datatype check functions are exported, so you get 2-in-1.

• ✅ Validate input using simple functional API
• ✅ Just 1.13k nano sized core library (ESM, gizpped)
• ✅ Tree-shakable and side-effect free, so probably just ~500 bytes in your app
• ✅ Isomorphic, runs on client and server
• ✅ Async from the ground up
• ✅ Works with scalar values, composed object form-data types
• ✅ Extemely fast
• ✅ Compatible with every framework/library
• ✅ Simple, composable validator logic
• ✅ Sequential mode (stop on first error (default))
• ✅ Full result mode (run all validations)
• ✅ Translatable error messages
• ✅ Arbitrary error message return types (e.g. JSX, VNode, etc.)
• ✅ Comes with a robust set of validator primitives
• ✅ First class TypeScript support
• ✅ 100% Unit Test coverage

• yarn: yarn add validalli
• npm: npm install validalli

import { validate, isEmpty, isUrlPath, isOneOf, type Validator } from 'validalli'

// compose your own validators based on core validators,
// this way, internationalization and custom errors are simple
// validators can also be async
export const isSlugCorrect: Validator = ({ value }) => {
  if (!isEmpty(value) && isUrlPath(value)) {
    return true
  }
  return `Slug looks invalid: ${value}`
}

// many validator functions are pretty simple, but need to
// use custom data to check against; this logic should also
// be unit testable. Writing your own validator functions helps alot.
export const isLanguageSupported: Validator = ({ value }) =>
  isOneOf(value, ['de', 'en']) : true ? `Language not supported: ${value}`

// user-provided input, aggregated as an object
const someFormState = {
  sitePath: '/foo-bar',
  language: 'fr',
}

// in default mode, validation stops with the first error that occurs
const validationState = await validate<NewPageModel>(someFormState, {
  sitePath: isSlugCorrect, // one or more validator function can be passed via Array
  language: isLanguageSupported,
})

// as 'fr' is not supported, the validationState would look like this:
/**
 * {
 *   isValid: false,
 *   sitePath: {
 *     isValid: true,
 *     states: [{ isValid: true }]
 *   },
 *   language: {
 *     isValid: false,
 *     message: 'Language not supported: fr',
 *     states: [{ isValid: false, message: 'Language not supported: fr' }]
 *   }
 * }
 */

const { getStorage } = require('validalli')

// same API like ESM variant

This is a validation library only. As every modern frontend framework supports some time of one-, two- or unidirectional data binding or even full-featured true reactivity, it should be rather easy to integrate this library in any application out there.

If you need help with integration, feel free to start a new discussion thread.