XHR to Fetch Migration Bug
XHR to Fetch Migration Bug
This article addresses the specific XHR deprecation/compatibility bug mentioned in Tutorial Episode 1, providing users with guidance on migrating from XMLHttpRequest to the Fetch API.
The Problem
Our application embeds JSON data directly into the build and uses a monkey-patched "fetch()" method to intercept requests and serve data from this embedded JSON. This allows the application to work offline and reduces server load.
However, when AI-generated code uses XMLHttpRequest (XHR) instead of "fetch()" to load data, it bypasses our monkey-patched fetch method entirely. The XHR requests attempt to load data from a remote server, which:
- Fails if the server is unavailable or the endpoint doesn't exist
- Bypasses the embedded JSON data we intended to serve
- Can cause unexpected errors or missing data in the application
Error Message
You may see an error like:
Uncaught SyntaxError: Failed to execute 'open' on 'XMLHttpRequest': invalid URL
The Solution
Ensure all data requests use the "fetch()" API instead of XMLHttpRequest. This allows our monkey-patched fetch to intercept the requests and serve the embedded JSON data as intended.
Before (Problematic)
// XHR bypasses our monkey-patched fetch
const xhr = new XMLHttpRequest();
xhr.open('GET', '/api/data.json');
xhr.onload = function() {
const data = JSON.parse(xhr.responseText);
};
xhr.send();
After (Correct)
// fetch() is intercepted by our monkey patch
const response = await fetch('/api/data.json');
const data = await response.json();
Why This Happens
AI code assistants are often trained on older codebases or documentation that still use XHR patterns. When generating code, they may default to XHR instead of the modern fetch API, unaware of our application's specific architecture that relies on fetch interception.
How to Fix in MakkoAI
If you encounter this error in your game:
- Copy the error message from the preview console
- Paste it into AI Chat
- Add this instruction: "instead of using xhr use fetch to fix this issue"
- Submit and let Makko fix the code
- Verify by checking the file and line mentioned in the error to confirm "fetch()" is now being used
After making the fix, rebuild your game in the preview panel and the error should be resolved.