BPM Scheduler

multi-scheduler.js

const createScheduler = (ctx, state) => {
  const callbacks = new Set();
  const id = setInterval(() => {
    const scheduleAheadTime = 0.1;
    while (state.time < ctx.currentTime + scheduleAheadTime) {
      callbacks.forEach((callback) => callback(state.beat, state.time));
      state.beat += 1;
      state.time += 60.0 / state.bpm;
    }
  }, 25);
  return {
    stop: () => clearInterval(id),
    schedule: (callback) => {
      callbacks.add(callback);
      return () => callbacks.delete(callback);
    },
  };
};


const ctx = new AudioContext();
const state = { bpm: 110, beat: 0, time: 0 };
const scheduler = createScheduler(ctx, state);

const stop = scheduler.schedule((beat, time) => {
  const osc = ctx.createOscillator();
  osc.frequency.value = beat % 2 ? 300 : 440;
  osc.start(time);
  osc.stop(time + 0.1);
  osc.connect(ctx.destination);
});

scheduler.js

const schedule = (ctx, state, callback) => {
  const id = setInterval(() => {
    const scheduleAheadTime = 0.1;
    while (state.time < ctx.currentTime + scheduleAheadTime) {
      state.time += 60.0 / state.bpm;
      state.beat += 1;
      callback(state.beat, state.time);
    }
  }, 25);
  return () => clearInterval(id);
};

const ctx = new AudioContext();
const state = { bpm: 110, beat: 0, time: 0 };

schedule(ctx, state, (beat, time) => {
  const osc = ctx.createOscillator();
  osc.frequency.value = beat % 2 ? 300 : 440;
  osc.start(time);
  osc.stop(time + 0.1);
  osc.connect(ctx.destination);
});