I suggest you build the sequencer in Max[1] or Pure Data[2]. Their advantages are:
1. You don't need to write any codes for UI objects
2. Simple things are faster to accomplish in these software.
3. For common complex tasks (fft etc.), Max or pd have built-in solutions that are likely better than the ones you build on your own.
4. You can script Max using js/lua/java. Hence if you want to build something complex and unusual, you can still fall back to programming.
5. You don't need to worry about timing in general. For example you can generate complex rhythm patterns in advance using lua/js/java and trigger them using Max/pd in real time. It will definitely perform better than some random web technology.
1. You don't need to write any codes for UI objects
2. Simple things are faster to accomplish in these software.
3. For common complex tasks (fft etc.), Max or pd have built-in solutions that are likely better than the ones you build on your own.
4. You can script Max using js/lua/java. Hence if you want to build something complex and unusual, you can still fall back to programming.
5. You don't need to worry about timing in general. For example you can generate complex rhythm patterns in advance using lua/js/java and trigger them using Max/pd in real time. It will definitely perform better than some random web technology.
[1]: https://cycling74.com/ [2]: http://puredata.info/