Fast XML Parser vs XML-JS vs XML2JSON: Performance and API Compared

When working with XML in modern JavaScript applications, you need a reliable way to convert data into JSON for easier handling. fast-xml-parser, xml-js, and xml2json all solve this problem, but they differ in speed, features, and long-term support. Let's compare how they handle real-world tasks.

🚀 Parsing Speed and API Design

fast-xml-parser is built for speed. It uses a single class to handle parsing and offers synchronous processing by default.

// fast-xml-parser: Fast synchronous parsing
const { XMLParser } = require("fast-xml-parser");
const parser = new XMLParser();
const result = parser.parse(xmlString);

xml-js provides a flexible convert function that handles options for attributes and text nodes.

// xml-js: Flexible conversion
const convert = require('xml-js');
const result = convert.xml2json(xmlString, { compact: false });

xml2json typically uses a callback pattern or simple function call, often wrapping older parsing logic.

// xml2json: Simple callback style
const xml2json = require('xml2json');
xml2json.parser(xmlString, function(err, result) {
  const json = JSON.parse(result);
});

🗂️ Data Structure Options: Compact vs Standard

How the library structures the JSON output matters for your downstream code.

fast-xml-parser gives you a clean standard object by default but lets you tweak attribute handling.

// fast-xml-parser: Custom attribute prefix
const parser = new XMLParser({
  ignoreAttributes: false,
  attributeNamePrefix: "@_"
});
const result = parser.parse(xmlString);

xml-js shines here with a "compact" mode that keeps the structure close to the XML tree.

// xml-js: Compact mode
const result = convert.xml2json(xmlString, { compact: true });
// Output: { root: { child: { _text: "value" } } }

xml2json usually outputs a fixed structure based on the underlying engine, with less control over shape.

// xml2json: Fixed structure
xml2json.parser(xmlString, function(err, result) {
  // Structure depends on internal implementation
  console.log(result);
});

🔒 Validation and Safety

Processing untrusted XML can be risky. Validation helps prevent errors or security issues.

fast-xml-parser includes a built-in validator to check XML before parsing.

// fast-xml-parser: Built-in validation
const { XMLValidator } = require("fast-xml-parser");
const isValid = XMLValidator.validate(xmlString);
if (isValid === true) { /* safe to parse */ }

xml-js relies on the underlying parser and does not offer explicit validation steps in its main API.

// xml-js: No built-in validation
// You must try-catch the convert function
try {
  convert.xml2json(xmlString);
} catch (e) { /* handle error */ }

xml2json provides basic error handling via callbacks but lacks advanced validation features.

// xml2json: Callback error handling
xml2json.parser(xmlString, function(err, result) {
  if (err) { /* handle error */ }
});

🛠️ Building XML from JSON

Sometimes you need to send data back as XML, not just read it.

fast-xml-parser includes a dedicated builder class for this task.

// fast-xml-parser: JSON to XML
const { XMLBuilder } = require("fast-xml-parser");
const builder = new XMLBuilder();
const xmlOutput = builder.build(jsonObject);

xml-js handles this with the same convert function using a different method name.

// xml-js: JSON to XML
const xmlOutput = convert.json2xml(jsonObject, { compact: false });

xml2json is primarily focused on parsing and often lacks a robust builder for the reverse process.

// xml2json: Limited build support
// Often requires separate library or manual string construction

📅 Maintenance and Future Proofing

Choosing a library means trusting its maintainers to fix bugs and keep up with Node.js changes.

fast-xml-parser is actively maintained with frequent updates and strong community support.

// fast-xml-parser: Active ecosystem
// Regular npm updates and issue resolution

xml-js is also well-maintained and widely used in production environments.

// xml-js: Stable maintenance
// Consistent updates for compatibility

xml2json has seen little activity in recent years and may not support modern Node.js features.

// xml2json: Legacy status
// Check npm page for last publish date before using

🤝 Similarities: Shared Ground Between Libraries

Despite their differences, these libraries share common goals and basic behaviors.

1. 🔄 Bidirectional Conversion

• All three aim to move data between XML and JSON formats.
• Useful for integrating with legacy SOAP APIs or RSS feeds.

// All support basic XML input
const xml = "<root>data</root>";
// parser.parse(xml) or convert.xml2json(xml)

2. ⚙️ Configuration Options

• Each allows some level of customization for attributes and text nodes.
• Helps match existing data structures in your app.

// All accept options objects
const options = { ignoreAttributes: true };
// parser = new XMLParser(options) or convert.xml2json(xml, options)

3. 🌐 Node.js and Browser Support

• All can run in Node.js environments.
• Most support bundling for browser use with tools like Webpack.

// All work in Node.js
const lib = require('package-name');

4. ✅ Error Handling

• All provide ways to catch malformed XML errors.
• Prevents crashes when data is incomplete.

// All require try-catch or callbacks
try { /* parse */ } catch (e) { /* handle */ }

5. 📦 Zero External Dependencies

• Most versions aim to be lightweight with few dependencies.
• Reduces risk in your supply chain.

// Check package.json for dependencies
// "dependencies": {} 

📊 Summary: Key Similarities

🆚 Summary: Key Differences

💡 The Big Picture

fast-xml-parser is like a high-performance engine 🏎️ — best for teams that need speed, validation, and modern features. Ideal for APIs, large data processing, and security-conscious apps.

xml-js is like a Swiss Army knife 🔪 — perfect for teams that need flexibility in data structure and bidirectional conversion. Great for general-purpose integration tasks.

xml2json is like an older tool 🧰 — usable for quick scripts or legacy maintenance, but not recommended for new architecture due to limited updates.

Final Thought: For most modern frontend and Node.js projects, fast-xml-parser or xml-js will serve you better. They offer active support and features that match today's development standards.