I believe typescript / js is missing standard library and find it rewarding to work during weekends on those lower level libraries/modules with no/low dependency fanout, publishing them here [0] when they're ready to see the light.
They're driven by what problems I see at work and while playing with other weekend projects so coverage may be asymmetric (some parts are well covered, others that should be are absent <<ie. documentation>>).
I find definition of success as just "working on it" very pleasant.