Waterfall with promises.

waterfall-metrics.js

function waterfall(tasks, callback) {
  var firstTask = tasks.shift();

  return tasks.reduce(function(prevPromise, task) {
    return prevPromise.then(function() {
      var args = Array.prototype.slice.call(arguments);
      args.unshift(task);
      return makePromise.apply(null, args);
    });
  }, makePromise(firstTask));
  
  function makePromise(task) {
    var args = Array.prototype.slice.call(arguments, 1);
    return new Promise(function(resolve) {
      function resolveProxy() {
        console.timeEnd(task.displayName);
        resolve.apply(null, arguments);
      }
      args.push(resolveProxy);
      console.time(task.displayName);
      var res = task.apply(null, args);
      if (res) resolveProxy(res);
    });
  }
}

waterfall.js

function waterfall(tasks, callback) {
  var firstTask = tasks.shift();

  return tasks.reduce(function(prevPromise, task) {
    return prevPromise.then(function() {
      var args = Array.prototype.slice.call(arguments);
      args.unshift(task);
      return makePromise.apply(null, args);
    });
  }, makePromise(firstTask));
  
  function makePromise(task) {
    var args = Array.prototype.slice.call(arguments, 1);
    return new Promise(function(resolve) {
      args.push(resolve);
      var res = task.apply(null, args);
      if (res) resolve(res);
    });
  }
}