How to Convert XML to JSON: Overcoming Attributes, Array Coercion, and Namespaces

The XML to JSON Impedance Mismatch

Converting XML documents into clean, developer-friendly JSON is challenging because XML and JSON model data with fundamentally different primitives. XML supports attributes on tags, mixed text-node children, namespaces, and unordered repeating elements. JSON only supports string keys mapped to primitives, arrays, or sub-objects.

The 3 Major Conversion Challenges

• Attributes vs Elements: An XML tag like <user id="42">John</user> has both an attribute (id) and text content (John). In JSON, this is typically converted using a prefix convention (e.g. {"@id": 42, "#text": "John"}).
• Array Coercion Trap: If an XML element has multiple child tags <item>1</item><item>2</item>, parsers output an array [1, 2]. However, if only one <item>1</item> exists, naive parsers output a single object {item: 1} instead of [1], breaking downstream array iteration.
• Type Inference: XML stores numbers and booleans as text strings. Modern converters must intelligently parse "true" as boolean true and "42" as number 42 without corrupting leading-zero strings like postal codes ("07030").

1. Converting XML in Node.js (fast-xml-parser)

fast-xml-parser is the gold standard for high-speed XML parsing in Node.js and TypeScript. It supports attribute prefixes, automatic number parsing, and explicit array guarantees:

import { XMLParser } from 'fast-xml-parser';

const xmlData = `
<store name="CoShareX Depot">
  <book id="101">
    <title>High Performance WebRTC</title>
    <price>39.99</price>
  </book>
  <book id="102">
    <title>Client-Side Cryptography</title>
    <price>49.99</price>
  </book>
</store>`;

const parser = new XMLParser({
  ignoreAttributes: false,
  attributeNamePrefix: '@_',
  parseAttributeValue: true,
  parseTagValue: true,
  isArray: (tagName) => tagName === 'book' // Guarantee array even if 1 book
});

const jsonOutput = parser.parse(xmlData);
console.log(JSON.stringify(jsonOutput, null, 2));

2. Converting XML in Python (xmltodict)

import json
import xmltodict

xml_content = """
<catalog>
    <product sku="A123">
        <name>Mechanical Keyboard</name>
        <in_stock>true</in_stock>
    </product>
</catalog>
"""

# Parse XML to Python Dictionary
data_dict = xmltodict.parse(
    xml_content,
    attr_prefix="@",
    force_list={'product'} # Ensure product is always a list
)

# Serialize to formatted JSON
json_output = json.dumps(data_dict, indent=2)
print(json_output)

3. Pure Browser Approach (DOMParser)

In client-side applications without external libraries, you can parse XML using the native DOMParser API and recursively traverse the DOM tree into a JavaScript object:

function xmlToDom(xmlString) {
  const parser = new DOMParser();
  const doc = parser.parseFromString(xmlString, 'text/xml');
  
  // Check for parser errors
  const parseError = doc.querySelector('parsererror');
  if (parseError) throw new Error('XML parsing failed: ' + parseError.textContent);
  
  return doc.documentElement;
}