I have to refactor a few very old TYPO3 extensions. they are compatible with ^4 but the company I'm working for now needs them for ^8 (the development for this extensions stopped for whatever reason).
I was wondering what is the best approach for me to get this task done -
are there some major resources I could use to get into that topic?
or a general changelog for TYPO3 extensions based on the version up from 4-9?
Any information is much appreciated.
Trying best to answer this, it's up to you how you maintain your site. Off course you need to check the complexity of the extension you build.
Check a few parameters below:
1. Complexity of the extension
Off course you have a big challenge to maintain code (Probably PI-Base extension). Your code should work with TYPO3 8.x as well as PHP 7.0.
2. Code Scalability
A simple thing, your code must be clean so understand better.
Now, you have two way to maintain your extension which is:
If you don't have complex application in your web site, you can follow @Aristeidis Karavas and rebuild the completely new extension (Extbase approach off course).
I'll recommend, re-develop for better quality product and to get optimized speed! What do you say?
For TER extension (which is available at extensions.typo3.org) might provide migration extension, such as EXT:tt_news to EXT:tx_news. For the custom extension, you can write your own SQL script which migrates your extension data to the new extension.
Compatibility Extension:
You can use compatibility extension available at TER which provide some easy solution to map TYPO3 classes.
Useful Links: Here is some useful link could bring you to the bright side and will make your stuff easier:
Hope this will help you!