XMLHttpRequest vs Fetch API — Comparative Analysis

When discussing HTTP requests in JavaScript, we have two main built-in options: XMLHttpRequest (XHR) and Fetch API. Although both serve the same purpose - to receive or send network data - their implementation methods and capabilities differ significantly. In this article, we'll conduct a comparative analysis to examine their differences, advantages, and disadvantages from a professional perspective.

---

1. Code Structure and Readability

      // XMLHttpRequest (XHR) 
     const xhr = new XMLHttpRequest(); xhr.open("GET", url); 
     xhr.onreadystatechange = () => {
        if (xhr.readyState === 4 && xhr.status === 200) {
            console.log(JSON.parse(xhr.responseText)); 
        } 
    };
    xhr.send();
    
    // Fetch API
    fetch(url)
    .then(response => response.json())
    .then(data => console.log(data));

Opinion: The Fetch API clearly has a simpler, shorter, and more readable structure, especially when using async/await.

---

2. Promise and async/await Support

• XHR: Doesn't use Promises at all. Requires working with callbacks.
• Fetch: Promise-based, easily integrates with async/await.

Conclusion: The Fetch API is more compatible with modern JavaScript workflows.

---

3. Advanced Control

• XHR: Supports complex control like progress events, configurable timeouts, abort() method.
• Fetch: Basic API lacks timeout and progress control (though AbortController can be used).

     // Fetch cancellation 
    const controller = new AbortController();
    const timeoutId = setTimeout(() => controller.abort(), 5000);
    
    try {
        const response = await fetch(url, { signal: controller.signal });
    } catch (error) {
        if (error.name === "AbortError") {
            console.log("Request timed out");
        }
    }

Conclusion: XHR provides more control "out of the box." With Fetch, you need to add it manually.

---

4. Response Processing

• XHR: Response comes as responseText (text) or responseXML. For JSON, requires JSON.parse().
• Fetch: Offers multiple methods: json(), text(), blob(), formData(), etc. - simple and convenient.

Conclusion: Fetch has a simpler and more convenient API for data parsing.

---

5. Browser Support and Compatibility

• XHR: Supported in nearly all browsers, including older IE versions.
• Fetch: Supported in modern browsers. Not available in IE.

Conclusion: If you're targeting older browsers, XHR might still be necessary.

---

Final Analysis

Criterion	XMLHttpRequest	Fetch API
Promise support	No	Yes
Code simplicity	Hard to read, callback-heavy	Simple and async-friendly
Timeout / Abort	Supported	Requires AbortController
Progress event	Supported	Not supported
Support in old browsers	Full	Partial (no IE)

Final conclusion: In modern applications where IE support isn't mandatory, the Fetch API is clearly the winner. It's simple, readable, cleaner, and fully compatible with modern async code. While XMLHttpRequest remains useful in certain cases where you need more control or support for older browsers.

---