the-json-library

The JSON Library

A lightweight JSON schema validation library for JavaScript that can be used in both browser and Node.js environments.

Features

• Validate JSON data against schemas
• No external dependencies
• Works in both browser and Node.js
• Supports common validation types and formats
• Comprehensive error reporting
• Small footprint
• Strict validation with additional properties control

Installation

npm install the-json-library

Usage

Basic Usage

import { validate } from 'the-json-library';

// Define a schema
const schema = {
  type: 'object',
  required: ['name', 'email'],
  properties: {
    name: { type: 'string' },
    email: { type: 'string', format: 'email' },
    age: { type: 'integer', minimum: 0 }
  }
};

// Validate some data
const data = {
  name: 'John Doe',
  email: '[e-mail]',
  age: 30
};

const result = validate(data);

if (result.isValid) {
  console.log('Validation successful!');
} else {
  console.error('Validation errors:', result.errors);
}

Static Validation

You can also use the static method without creating an instance:

import { validate } from 'the-json-library';

const result = validate(data, schema);

if (result.isValid) {
  console.log('Validation successful!');
} else {
  console.error('Validation errors:', result.errors);
}

Additional Properties Control

By default, the library rejects any properties not defined in the schema:

// Schema only defines name and email
const schema = {
  type: 'object',
  properties: {
    name: { type: 'string' },
    email: { type: 'string' }
  }
};

// Data contains an extra property 'age'
const data = {
  name: 'John Doe',
  email: '[e-mail]',
  age: 30  // This will cause validation failure
};

const result = validate(data, schema);
// result.isValid will be false
// result.errors will contain an error about 'age' being an additional property

To allow additional properties, set additionalProperties to true:

const schema = {
  type: 'object',
  properties: {
    name: { type: 'string' },
    email: { type: 'string' }
  },
  additionalProperties: true  // Allow any additional properties
};

// Now this will pass validation
const data = {
  name: 'John Doe',
  email: '[e-mail]',
  age: 30  // This is now allowed
};

You can also provide a schema for additional properties:

const schema = {
  type: 'object',
  properties: {
    name: { type: 'string' },
    email: { type: 'string' }
  },
  // All additional properties must be numbers
  additionalProperties: { type: 'number' }
};

// This will pass validation
const data = {
  name: 'John Doe',
  email: '[e-mail]',
  age: 30,  // Valid additional property (number)
  score: 95  // Valid additional property (number)
};

Validation Result

The validation result contains:

• isValid - boolean indicating if the validation passed
• errors - array of error objects with:
  • path - the path to the property that failed validation
  • message - description of the error

Supported Schema Features

Types

• string
• number
• integer
• boolean
• array
• object
• null

String Validations

• minLength / maxLength - string length constraints
• pattern - regular expression pattern
• format - predefined formats (email, date, date-time, uri)

Number Validations

• minimum / maximum - value constraints

Object Validations

• properties - schema for each property
• required - list of required properties
• additionalProperties - controls whether properties not defined in the schema are allowed

Array Validations

• items - schema for array items

Other Validations

• enum - list of allowed values

Schema Format

Schemas should follow a simplified JSON Schema format. Here's an example of a more complex schema:

{
  "type": "object",
  "required": ["id", "name", "metadata"],
  "properties": {
    "id": { "type": "integer" },
    "name": { "type": "string", "minLength": 1 },
    "email": { "type": "string", "format": "email" },
    "tags": {
      "type": "array",
      "items": { "type": "string" }
    },
    "metadata": {
      "type": "object",
      "properties": {
        "created": { "type": "string", "format": "date-time" },
        "status": { "enum": ["active", "inactive", "pending"] }
      },
      "additionalProperties": false
    }
  },
  "additionalProperties": false  // No additional root properties allowed
}

License

MIT