Check out the interface of my webmidi API midisequenser, it is far from ready must cleanup to early and late notes during recording, making a visual editor for canvas, and load save.
It is pretty much an old school midisequenser with a little easier UI, then the old school ones. And some "nice?" graphic to accompany. Maybe a tool for kids starting recording.

It is and will be all clientside, see URL

JT64