A rudimentary, asychronous ES5 generator using Promises

asyn-sequence.js

/**
 * Return a random number between min/max where the mean
 * result is approximately the mode across a uniform distribution.
 * @param min {Number} - lower limit of range (inclusive)
 * @param max {Number} - upper limit of range (inclusive)
 * @return {Function} - a function that returns a random number between 'min' and 'max'
 */
var genRandomFromRangeFn = function(min, max) {
    return function() {
        var res = Math.round(Math.random() * (max - min)) + min;
        return res;
    };
};

/**
 * Async Function Generator: generates a function that returns a Promise that when
 * resolved will have happend after a random interval in 'ms' between
 * 'min' and 'max' (see #genRandomFromRangeFn) 
 * @param min {Number} - lower limit of range to generate random number within
 * @param max {Number} - upper limit of range to generate random number within
 * @return {Promise} - when fulfilled, it's value property will have
 *          two properties: iteration {Number} - the count for this value in sequence with the others
 *                          period: {Number} - number of milliseconds waited before resolving
 */
var timedSequenceGenerator = function(min, max) {
    var randomFromRange = genRandomFromRangeFn(min, max),    // get a random number between min and max
        count = 1;

    return {
        next: function() {
            return new Promise(function(resolve, reject) {
                // generate a random time period to wait between min,max (in ms)
                var wait = randomFromRange() * 1000;
                setTimeout(function() {
                    resolve({ value: { iteration: count++, period: wait }, done: false });
                    // console.log("[debug] iteration: %d, wait time = %d", count, wait);
                }, wait);
            });
        }
    };
};

var sequencer = timedSequenceGenerator(6, 9),
    prev_promise = Promise.resolve(),
    max_refresh = 20,
    periods = [];

// Run a random wait period generated by sequence.next() for
// max_refresh times, in series (back to back).    
while (max_refresh--) {
  prev_promise = prev_promise.then(function() {
      return sequencer.next();
  })
  .then(function(int) {
      console.log("here");
      console.log("tick (%d) waited %d ms", int.value.iteration, int.value.period)
  })
  .catch(function(err) {
      console.log("error: ", err);
  });
}