How to Fix Slow XML Parsing in React Native

If you've ever parsed XML in a React Native app, you've probably noticed the pain: your UI freezes, animations stutter, and users wait. The culprit? JavaScript XML parsers run on the JS thread, blocking everything else.

I hit this problem on a project where XML parsing took over 8 seconds on low-end Android devices. After moving to a native solution, it dropped to under 2 seconds. You can read the full case study here. Here's how to fix it.

Why JavaScript XML Parsing Is Slow

Popular libraries like react-native-xml2js work fine for small files. But they have a fundamental problem: they run on the single JavaScript thread.

While parsing happens, your app can't:

• Respond to touch events
• Update animations
• Render UI changes

On older devices or with large XML files, this means frozen screens and angry users.

The Solution: Native XML Parsing

Native code (Kotlin on Android, Swift on iOS) can parse XML on a background thread. The JS thread stays free, your UI stays responsive.

You have two options:

1. Build your own native module
2. Use an existing library

Option 1: Use react-native-turboxml

I built react-native-turboxml to solve this exact problem. It's a TurboModule that parses XML natively using Kotlin coroutines on Android.

Installation

npm install react-native-turboxml
# or
yarn add react-native-turboxml

Usage

import { parseXml } from 'react-native-turboxml';

const xmlString = `
  <root>
    <item id="1">First</item>
    <item id="2">Second</item>
  </root>
`;

const result = await parseXml(xmlString);
console.log(result);

That's it. The parsing happens on a background thread, returns a JavaScript object, and your UI never blocks.

Benchmarks

Testing with a 500KB XML file on a budget Android device:

Library	Time	UI Blocking
react-native-xml2js	3.2s	Yes
react-native-turboxml	0.9s	No

The time improvement is nice, but the real win is zero UI blocking.

Option 2: Build Your Own Native Module

If you need custom parsing logic, here's the approach.

Android (Kotlin)

Create a native module using Kotlin coroutines and Jackson's XmlMapper:

@ReactMethod
fun parseXml(xmlString: String, promise: Promise) {
    CoroutineScope(Dispatchers.IO).launch {
        try {
            val xmlMapper = XmlMapper()
            val result = xmlMapper.readValue<Map<String, Any?>>(xmlString)
            val writableMap = convertToWritableMap(result)
            promise.resolve(writableMap)
        } catch (e: Exception) {
            promise.reject("PARSE_ERROR", e.message)
        }
    }
}

Key points:

• Dispatchers.IO runs parsing off the main thread
• Jackson handles the XML-to-Map conversion
• Return a WritableMap to cross the JS bridge

iOS (Swift)

Similar approach using XMLParser on a background queue:

@objc func parseXml(_ xmlString: String, resolver: @escaping RCTPromiseResolveBlock, rejecter: @escaping RCTPromiseRejectBlock) {
    DispatchQueue.global(qos: .userInitiated).async {
        // Parse XML here
        // Convert to dictionary
        DispatchQueue.main.async {
            resolver(resultDictionary)
        }
    }
}

When to Use Native XML Parsing

Not every project needs this. Use native parsing when:

• XML files are larger than 50-100KB
• You're targeting low-end devices
• Parsing happens during user interaction
• You're parsing multiple files

For small config files parsed once at startup, JavaScript parsers are fine.

Other Performance Wins

While you're optimizing XML handling, consider these:

Parallelize with Promise.all

If you're fetching and parsing multiple files:

// Slow - sequential
const data1 = await parseXml(xml1);
const data2 = await parseXml(xml2);
const data3 = await parseXml(xml3);

// Fast - parallel
const [data1, data2, data3] = await Promise.all([
    parseXml(xml1),
    parseXml(xml2),
    parseXml(xml3),
]);

Cache Parsed Results

Don't parse the same XML twice:

const cache = new Map<string, ParsedData>();

async function getParsedXml(key: string, xmlString: string) {
    if (cache.has(key)) {
        return cache.get(key);
    }
    const result = await parseXml(xmlString);
    cache.set(key, result);
    return result;
}

Consider Your Data Format

If you control the data source, JSON is faster than XML in JavaScript. But if you're stuck with XML from an API or legacy system, native parsing is your best option.

Conclusion

JavaScript XML parsers block your thread and hurt performance. Moving parsing to native code with Kotlin coroutines or Swift's GCD keeps your UI responsive.

The easiest fix: install react-native-turboxml and replace your parser calls.

If you're dealing with performance issues beyond XML parsing, check out my other articles on React Native optimization.

---

Have questions or found this helpful? Find me on GitHub or LinkedIn.