I know that the Journaled File System (JFS) does only journaling of the metadata.
But does JFS under Linux work like the ext3 writeback mode or like the ordered mode?
It is similar to ordered mode as per Journaling file systems.
So it works like ordered mode.
For a more detailed comparison you can browse the source of inode.c for JFS and inode.c for ext3, along with other files in the respective filesystem directories.