XML Helper Library

A comprehensive TypeScript library for XML parsing, validation, and conversion built from scratch without external dependencies.

Features

• ✅ XSD Schema Validation: Load and validate XML documents against XSD schemas
• 🔄 XML ↔ JSON Conversion: Convert between XML and JSON formats with customizable options
• 📝 XML Parsing: Parse XML documents into structured node trees
• 🛡️ Error Handling: Detailed error reporting with line numbers and error codes
• 🎯 TypeScript Support: Full TypeScript support with comprehensive type definitions
• 🚀 Zero Dependencies: Built from scratch without external libraries

Installation

npm install
npm run build

Quick Start

import XmlHelper from './src/index';

const xmlHelper = new XmlHelper();

// Load XSD schema
const schemaErrors = xmlHelper.loadSchema(xsdContent);
if (schemaErrors.length === 0) {
  console.log('Schema loaded successfully!');
}

// Validate XML
const validationErrors = xmlHelper.validateXml(xmlContent);
if (validationErrors.length === 0) {
  console.log('XML is valid!');
}

// Convert XML to JSON
const result = xmlHelper.xmlToJson(xmlContent);
if (result.success) {
  console.log('JSON:', result.data);
}

// Convert JSON to XML
const xmlString = xmlHelper.jsonToXml(jsonData, 'root');
console.log('XML:', xmlString);

API Reference

XmlHelper Class

The main class that provides all XML processing functionality.

Methods

loadSchema(xsdContent: string): ValidationError[]

Loads and parses an XSD schema for validation.

• Parameters:
  • xsdContent: The XSD schema content as a string
• Returns: Array of validation errors (empty if successful)

validateXml(xmlContent: string): ValidationError[]

Validates XML content against the loaded schema.

• Parameters:
  • xmlContent: The XML content to validate
• Returns: Array of validation errors with line numbers

xmlToJson(xmlContent: string, options?: XmlToJsonOptions): XmlParseResult

Converts XML to JSON format.

• Parameters:
  • xmlContent: The XML content to convert
  • options: Optional conversion settings
• Returns: Parse result with success flag, data, and errors

jsonToXml(jsonData: any, rootElement?: string, options?: JsonToXmlOptions): string

Converts JSON data to XML format.

• Parameters:
  • jsonData: The JSON data to convert
  • rootElement: Optional root element name
  • options: Optional conversion settings
• Returns: XML string

parseXml(xmlContent: string): { node: XmlNode | null; errors: ValidationError[] }

Parses XML without schema validation.

• Parameters:
  • xmlContent: The XML content to parse
• Returns: Object with parsed node and errors

Types

ValidationError

interface ValidationError {
  line: number;        // Line number where error occurred
  column: number;      // Column number where error occurred
  message: string;     // Error description
  code: string;        // Error code identifier
}

XmlToJsonOptions

interface XmlToJsonOptions {
  preserveAttributes?: boolean;    // Include XML attributes (default: true)
  attributePrefix?: string;        // Prefix for attributes (default: '@')
  textKey?: string;               // Key for text content (default: '#text')
  ignoreNamespaces?: boolean;     // Ignore XML namespaces (default: false)
}

JsonToXmlOptions

interface JsonToXmlOptions {
  attributePrefix?: string;        // Prefix for attributes (default: '@')
  textKey?: string;               // Key for text content (default: '#text')
  rootElement?: string;           // Root element name (default: 'root')
  declaration?: boolean;          // Include XML declaration (default: true)
  indent?: string;                // Indentation string (default: '  ')
}

Examples

Schema Validation

const xsdSchema = `<?xml version="1.0" encoding="UTF-8"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema">
  <xs:element name="person">
    <xs:complexType>
      <xs:sequence>
        <xs:element name="name" type="xs:string"/>
        <xs:element name="age" type="xs:int"/>
      </xs:sequence>
    </xs:complexType>
  </xs:element>
</xs:schema>`;

const xmlHelper = new XmlHelper();
const errors = xmlHelper.loadSchema(xsdSchema);

if (errors.length === 0) {
  const validationErrors = xmlHelper.validateXml(`
    <person>
      <name>John Doe</name>
      <age>30</age>
    </person>
  `);
  
  console.log('Valid:', validationErrors.length === 0);
}

XML to JSON Conversion

const xml = `
<library>
  <book id="1" category="fiction">
    <title>The Great Gatsby</title>
    <author>F. Scott Fitzgerald</author>
    <price>12.99</price>
  </book>
</library>`;

const result = xmlHelper.xmlToJson(xml, {
  preserveAttributes: true,
  attributePrefix: '@'
});

// Result:
// {
//   "library": {
//     "book": {
//       "@id": "1",
//       "@category": "fiction",
//       "title": "The Great Gatsby",
//       "author": "F. Scott Fitzgerald",
//       "price": 12.99
//     }
//   }
// }

JSON to XML Conversion

const json = {
  person: {
    '@id': 'p1',
    name: 'Jane Smith',
    details: {
      age: 25,
      city: 'New York'
    },
    hobbies: ['reading', 'swimming']
  }
};

const xml = xmlHelper.jsonToXml(json);

// Result:
// <?xml version="1.0" encoding="UTF-8"?>
// <person id="p1">
//   <name>Jane Smith</name>
//   <details>
//     <age>25</age>
//     <city>New York</city>
//   </details>
//   <hobbies>reading</hobbies>
//   <hobbies>swimming</hobbies>
// </person>

Error Handling

The library provides detailed error information including:

• Line and column numbers for precise error location
• Descriptive error messages explaining what went wrong
• Error codes for programmatic error handling

Common error codes:

• PARSE_ERROR: XML parsing failed
• SCHEMA_ERROR: XSD schema is invalid
• ELEMENT_NOT_FOUND: Required element missing
• INVALID_ATTRIBUTE_VALUE: Attribute value doesn't match type
• MIN_OCCURS_VIOLATION: Element occurs fewer times than required
• MAX_OCCURS_VIOLATION: Element occurs more times than allowed

Testing

Run the test suite to see all functionality in action:

npm run build
npm test

The test file (src/test.ts) demonstrates:

• Schema loading and validation
• XML parsing and validation
• XML to JSON conversion
• JSON to XML conversion
• Error handling scenarios

Architecture

The library is organized into focused modules:

• XmlParser: Core XML parsing functionality
• XsdParser: XSD schema parsing and interpretation
• XmlValidator: XML validation against XSD schemas
• XmlToJsonConverter: XML to JSON transformation
• JsonToXmlConverter: JSON to XML transformation
• XmlHelper: Main facade class combining all functionality

License

MIT License - feel free to use in your projects!

Contributing

This is a from-scratch implementation without external dependencies. Contributions are welcome for:

• Additional XSD features
• Performance improvements
• Bug fixes
• Enhanced error messages
• More validation rules