So you've got an XML payload and you need JSON. Sounds trivial until you realize XML and JSON have fundamentally different data models. XML has attributes, mixed content, namespaces, and implicit arrays. JSON has none of that baggage. A naive string-replacement or a default `xmltodict.parse()` call will technically "work", but your resulting JSON will be inconsistent, break on edge cases, and drive you mad two weeks from now when the payload changes. Here's how to do it properly. ## Why XML → JSON Isn't Just Find & Replace Before we get into the code, understand the core structural mismatches: | XML Concept | JSON Equivalent | Problem | |---|---|---| | Attributes (`id="123"`) | Properties | JSON has no attribute concept | | Single vs. multiple child elements | Value vs. Array | Single item = string, multiple = array. Inconsistent | | All text is a string | Typed values | `"true"`, `"42"` need real type inference | | Namespaces (`soap:Body`) | No equivalent | Naming conflicts without careful handling | These mismatches cause the majority of bugs in XML-to-JSON pipelines. Let's tackle each one. --- ## Challenge 1: Handling Attributes XML attributes don't have a natural home in JSON. The most portable convention is the **`@` prefix**: ```xml John Doe ``` Converts to: ```json { "user": { "@id": "123", "@role": "admin", "#text": "John Doe" } } ``` Using `fast-xml-parser` in Node.js: ```javascript import { XMLParser } from 'fast-xml-parser'; const parser = new XMLParser({ ignoreAttributes: false, // Don't throw away attributes! attributeNamePrefix: "@", // Prefix attributes with @ textNodeName: "#text", // Name for the text content parseAttributeValue: true // Auto-convert "123" → 123 }); const json = parser.parse(xmlString); ``` **Don't set `ignoreAttributes: true`** (which is the default in many libraries). You'll silently lose data like IDs, currency codes, and statuses that are often encoded as attributes in real-world XML. --- ## Challenge 2: Arrays The Silent Killer This is the one that bites everyone. XML doesn't differentiate between a collection with one item and a collection with many: ```xml Widget A Widget A Widget B ``` Without explicit configuration, most parsers turn these into different types: ```json // One item → string (bad!) { "products": { "product": "Widget A" } } // Multiple items → array (what you'd expect) { "products": { "product": ["Widget A", "Widget B"] } } ``` This silently breaks your frontend code whenever a single-item edge case comes through. **Your code does `products.product.map(...)` and suddenly crashes.** ### The Fix: Declare Your Array Tags ```javascript const parser = new XMLParser({ ignoreAttributes: false, attributeNamePrefix: "@", isArray: (tagName) => { // These tags should ALWAYS be arrays, even with a single child const alwaysArrayTags = ['product', 'item', 'user', 'order', 'tag', 'role']; return alwaysArrayTags.includes(tagName); } }); ``` If you don't know the schema upfront, write a post-processing step that wraps known plural parent containers: ```javascript function normalizeArrays(obj, arrayKeys = ['products', 'items', 'users', 'orders']) { if (typeof obj !== 'object' || obj === null) return obj; for (const key of Object.keys(obj)) { if (arrayKeys.includes(key) && !Array.isArray(obj[key])) { obj[key] = [obj[key]]; // Force it to be an array } normalizeArrays(obj[key], arrayKeys); } return obj; } ``` --- ## Challenge 3: Type Inference XML treats everything as text. That means `"true"`, `"false"`, `"42"`, and `"3.14"` are all strings unless you explicitly parse them. The `parseAttributeValue: true` option in `fast-xml-parser` handles attributes, but element text content also needs care: ```javascript function parseTypedValue(value) { if (value === "true") return true; if (value === "false") return false; if (value === "null" || value === "") return null; const num = Number(value); if (!isNaN(num) && value.trim() !== "") return num; return value; // Fallback: keep as string } ``` Or configure it directly in the parser: ```javascript const parser = new XMLParser({ ignoreAttributes: false, attributeNamePrefix: "@", parseAttributeValue: true, parseTagValue: true, // Also parses element text content trimValues: true // Trim whitespace from values }); ``` --- ## Real-World Scenario: SOAP to REST Migration One of the most common XML-to-JSON jobs is stripping SOAP envelope overhead when migrating to REST. Here's the pattern: **Incoming SOAP XML:** ```xml John Doe john@example.com admin user ``` **Target REST JSON:** ```json { "user": { "id": 123, "name": "John Doe", "email": "john@example.com", "roles": ["admin", "user"] } } ``` Here's a clean Node.js transformation: ```javascript import { XMLParser } from 'fast-xml-parser'; function soapToRest(soapXml) { const parser = new XMLParser({ ignoreAttributes: false, attributeNamePrefix: "@", parseAttributeValue: true, parseTagValue: true, isArray: (name) => name === 'Role' }); const parsed = parser.parse(soapXml); // Drill past the SOAP envelope wrapper const rawUser = parsed?.['soap:Envelope']?.['soap:Body']?.User; if (!rawUser) throw new Error("Could not locate User in SOAP body"); return { user: { id: rawUser["@id"], name: rawUser.Name, email: rawUser.Email, roles: rawUser.Roles.Role.map(r => r.toLowerCase()) } }; } ``` --- ## Real-World Scenario: XML Config to JSON Config If you're migrating an app from XML-based config (Spring, Maven, etc.) to JSON, you need proper type inference or your app will fail to read `port` as a number: **XML Config:** ```xml myapp true 10 ``` **Expected JSON Config:** ```json { "database": { "host": "localhost", "port": 5432, "name": "myapp", "ssl": true, "pool_size": 10 } } ``` ## Tools and Libraries ### JavaScript/Node.js ```javascript import { XMLParser } from 'fast-xml-parser'; const parser = new XMLParser({ ignoreAttributes: false, parseAttributeValue: true, attributeNamePrefix: "@" }); const json = parser.parse(xmlString); ``` ### Python ```python import xmltodict import json with open('file.xml', 'r') as f: xml_content = f.read() json_data = xmltodict.parse(xml_content) print(json.dumps(json_data, indent=2)) ``` ### Online Tools Use our [XML to JSON converter](https://devtoollab.com/tools/xml-to-json) for quick conversions. It processes files locally for privacy. For teams that need to go further and load XML data directly into a relational database rather than JSON, an [XML to SQL converter](https://sonra.io/xml-to-sql-database-converter/) handles the full pipeline, including XSD-aware schema mapping and normalized table output for platforms like Snowflake, BigQuery, and SQL Server. ## Conclusion Pick one attribute strategy and stick with it. The @ prefix works well. Handle arrays consistently always use arrays for collections. Implement type conversion to preserve numbers and booleans. Test with real data and handle errors gracefully. For the reverse process, read our [JSON to XML Conversion Guide](/blog/json-to-xml-conversion-guide). Check out [Essential Developer Tools](/blog/essential-developer-tools) for more utilities.

xml json data transformation developer guide

XML to JSON Conversion: Best Practices and Common Pitfalls