How do I troubleshoot polyfills in my JavaScript project?

I'm having issues with polyfills in my JavaScript project. How can I troubleshoot them?

First, can you specify which polyfills you're using and what issues you're encountering?

I'm using core-js for Promise and Fetch, but they don't seem to be working in older browsers.

Make sure you've included the polyfill scripts before your main JavaScript file. Have you checked the browser compatibility?

Yes, but I'm still getting errors. What should I do next?

Try checking the console for specific error messages. They can provide clues about what's going wrong.

I see a 'Promise is not defined' error. What does that mean?

It means the polyfill for Promise isn't being loaded correctly. Double-check the script tag order and ensure core-js is included.