The EXTJ forum was closed by the owners at the end of last year, they have gone thru a difficult time taking care of their elderly parents and were just worn out.
Some of the friends are trying to get some other sites going, I am listing two of them. It seems rather difficult, since they are competing against each other; none has reached 100 members yet.
I am listing also the blog of JHK, it has going on for many years and has excellent material and following.