Why there is no option to combine JS files?

FlyingPress doesn't provide an option to combine/contact JavaScript files. This is intentional, for performance!

• With http/2, combining is not recommended. Browser doesn't have to wait and parse a large file. Smaller files are better.
• Combining will result in lower cache hit ratio in both browser cache and CDN cache. This is because whenever a single file is updated, the whole JS file needs to be downloaded again. When not combined, only the file changed will be downloaded.
• This can dramatically increase cache size, cache build time and increased resource usage in your server.
• Every time we purge, it encourages chances of another 404 for Search Engine crawlers.

Google PageSpeed Insights will never show a recommendation to combine JavaScript files. GTmetrix also removed this recommendation in April 2020.

Few resources:

• GTmetrix: Recommendation Updates – HTTP/2 changes and more
• WPJohnny: Why You SHOULDN’T Combine CSS & JS (Performance Reasons)