This is a simple app that lets you define spin workouts in a JavaScript file. When running, it shows the cadence and resistance for the current and upcoming interval, as well as a clock for the current interval and total time remaining.

To create workouts, edit workouts.js to add new workouts:

// d=duration, c=cadence, r=resistance
const workouts = {
  myWorkout: {
    intervals: [
      { d: 5, c: 75, r: 30 },
      { d: 4, c: 60, r: 50 },
      { d: 3, c: 75, r: 30 },
      { d: 2, c: 60, r: 50 },
      { d: 7, c: 75, r: 25 },
    ]
  },
  ...
};

Then open index.html in a browser and specify your workout in the URL hash, e.g.

/path/to/index.html#myWorkout
                    ^^^^^^^^^

To restart the workout, just refresh the page.