We're all inspired by other things, and being first doesn't really count for much if you don't promote yourself. Even then, it's a roll of the dice as to if you stand out in the crowd.
If you're just going by "JS-based grid sequencer' I created one in February 2011 as part of an HTML-based emulation of a Boss DR-110 drum machine (Which I later updated to use the Web Audio API to synthesize the drum voices)
https://github.com/leviathant/BossDR110
It's skeumorphic (I was challenging the popular notion "You can do everything in HTML that you can do in Flash" at the time - it wasn't true then, but we're much closer now), I never finished out 'song mode', but it is a JS-based grid sequencer that predates your timeline. As best as I can tell, it was the first click-and-drag Javascript knob done Rebirth/Reason style - it was a little clunky, but I sure as hell couldn't find any remotely similar code to base it off of - but I don't get bent out of shape whenever I see other people making Javascript knobs.