Repeat an action `max` number of times or `until` some condition, with optional `delay` between repetitions

repeat.js

/**
 * Repeat an action
 * @param {Object} opt - options
 * @param {Function} opt.action - action to repeat
 * @param {Function} opt.until - termination condition
 * @param {Number} opt.delay - delay between actions
 * @param {Number} opt.max - maximum number of repetitions
 * @returns {Promise}
 */
function repeat(opt) {
  if (!opt || !opt.action) throw new Error("Missing action")
  return iter(1)
  function iter(n) {
    return Promise.resolve()
      .then(opt.action)
      .then(function(result) {
        if (opt.until && opt.until(result)) return result
        if (opt.max && n >= opt.max) return result
        if (!opt.delay) return iter(n+1)
        return new Promise(function(f) {setTimeout(f, opt.delay)}).then(iter.bind(null, n+1))
      })
  }
}