@hyperfrontend/json-utils

Zero-dependency JSON Schema Draft v4 validation and schema generation utilities.

What is @hyperfrontend/json-utils?

@hyperfrontend/json-utils provides lightweight utilities for validating JSON data against JSON Schema Draft v4 specifications and generating schemas from JavaScript values via a functional-programming-first implementation.

The library provides two core capabilities: validation (checking if data conforms to a schema) and generation (creating a schema from sample data). Both functions use pure functional design with no side effects, making them predictable and easy to test.

Key Features

• Full JSON Schema Draft v4 Support - Validates type, properties, required, items, enum, pattern, minimum/maximum, allOf/anyOf/oneOf/not, $ref, format, and more
• Schema Generation - Create schemas from sample data with configurable array handling modes
• Reusable Validators - Create validator functions once, reuse them efficiently
• Detailed Error Messages - Get precise error paths, messages, and codes for failed validations
• Zero External Dependencies - Self-contained implementation with no third-party runtime dependencies
• Isomorphic Design - Works identically in Node.js and browser environments

What This Library Does NOT Support

• JSON Schema Draft 6, 7, 2019-09, or 2020-12 - Only Draft v4 is implemented
• External $ref Resolution - Only internal references (#/definitions/...) are supported; no HTTP or file-based schema loading
• const, contains, propertyNames, if/then/else - These are Draft 6+ features
• Custom Format Validators - Built-in formats only (email, uri, date-time, etc.)

If you need full JSON Schema support across multiple draft versions, consider Ajv. This library is intentionally scoped for Draft v4 use cases where a lightweight, zero-dependency solution is preferred.

Why Use @hyperfrontend/json-utils?

Validate User-Provided Schemas

When your application accepts user-defined JSON Schema (like contract definitions or API specifications), you need reliable validation. This library validates both the data and can verify that schemas themselves are valid Draft v4 documents using the meta-schema.

Generate Schemas from Sample Data

Instead of manually writing schemas for data structures, generate them from representative samples. Useful for testing, documentation generation, and bootstrap schema creation.

Functional Programming Approach

All functions are pure with no side effects. Create validator functions with createValidator() and reuse them without worrying about shared state. Validation contexts are immutable and composable.

Installation

npm install @hyperfrontend/json-utils

Quick Start

Validate Data Against a Schema

import { validate } from '@hyperfrontend/json-utils'
import type { Schema } from '@hyperfrontend/json-utils'

const schema: Schema = {
  type: 'object',
  properties: {
    name: { type: 'string', minLength: 1 },
    age: { type: 'integer', minimum: 0 },
    email: { type: 'string', format: 'email' },
  },
  required: ['name', 'email'],
}

const result = validate({ name: 'Alice', email: 'alice@example.com' }, schema)
console.log(result.valid) // true

const invalid = validate({ name: '', age: -5 }, schema)
console.log(invalid.valid) // false
console.log(invalid.errors)
// [
//   { message: 'Missing required property: email', path: '/', code: 'required' },
//   { message: 'String must be at least 1 characters, got 0', path: '/name', code: 'minLength' },
//   { message: 'Number must be at least 0, got -5', path: '/age', code: 'minimum' }
// ]

Create Reusable Validators

import { createValidator } from '@hyperfrontend/json-utils'

const validateUser = createValidator({
  type: 'object',
  properties: {
    id: { type: 'integer' },
    username: { type: 'string', pattern: '^[a-z0-9_]+$' },
  },
  required: ['id', 'username'],
})

// Reuse without re-parsing schema
validateUser({ id: 1, username: 'alice' }) // { valid: true, errors: [] }
validateUser({ id: 'bad' }) // { valid: false, errors: [...] }

Generate Schemas from Data

import { toJsonSchema } from '@hyperfrontend/json-utils'

const data = {
  users: [
    { name: 'Alice', active: true },
    { name: 'Bob', active: false },
  ],
  metadata: { version: '1.0' },
}

const schema = toJsonSchema(data)
// {
//   type: 'object',
//   properties: {
//     users: {
//       type: 'array',
//       items: {
//         type: 'object',
//         properties: {
//           name: { type: 'string' },
//           active: { type: 'boolean' }
//         },
//         required: ['name', 'active']
//       }
//     },
//     metadata: {
//       type: 'object',
//       properties: { version: { type: 'string' } },
//       required: ['version']
//     }
//   },
//   required: ['users', 'metadata']
// }

Use $ref for Reusable Definitions

import { validate } from '@hyperfrontend/json-utils'

const schema = {
  definitions: {
    address: {
      type: 'object',
      properties: {
        street: { type: 'string' },
        city: { type: 'string' },
      },
      required: ['street', 'city'],
    },
  },
  type: 'object',
  properties: {
    home: { $ref: '#/definitions/address' },
    work: { $ref: '#/definitions/address' },
  },
}

validate(
  {
    home: { street: '123 Main', city: 'Boston' },
    work: { street: '456 Oak', city: 'Cambridge' },
  },
  schema
) // { valid: true, errors: [] }

API Overview

Validation

• validate(instance, schema, options?): ValidationResult - Validate a value against a JSON Schema
• createValidator(schema, options?): (data) => ValidationResult - Create a reusable validator function

Generation

• toJsonSchema(value, options?): Schema - Generate a JSON Schema from a JavaScript value

Types

• Schema - TypeScript interface representing JSON Schema Draft v4
• JsonType - 'string' | 'number' | 'integer' | 'boolean' | 'array' | 'object' | 'null'
• ValidationResult - { valid: boolean, errors: ValidationError[] }
• ValidationError - { message: string, path: string, code?: string, instance?: unknown, params?: object }
• ValidateOptions - { collectAllErrors?: boolean } - When false, stops at first error
• GenerateOptions - { arrays?: { mode: 'all' | 'first' | 'uniform' }, includeRequired?: boolean }

Supported Keywords

Compatibility

Output Formats

CDN Usage

<!-- unpkg -->
<script src="https://unpkg.com/@hyperfrontend/json-utils"></script>

<!-- jsDelivr -->
<script src="https://cdn.jsdelivr.net/npm/@hyperfrontend/json-utils"></script>

<script>
  const { validate, toJsonSchema } = HyperfrontendJsonUtils
</script>

Global variable: HyperfrontendJsonUtils

Dependencies

None — zero external dependencies.

Part of hyperfrontend

This library is part of the hyperfrontend monorepo.

📖 Full documentation

License

MIT