Run a function on each member of an array (like reduce) but use promises to chain them together asynchronusly

PromiseChain.js

  /**
   * Makes chain of promises
   * @param  {function} toRun     Function to apply to each item
   * @param  {array} processArray Array of items to process
   * @return {promise}            Final promise to pass on
   */
  chain: function(toRun, processArray) {
    var defer = Q.defer();
    var args = Array.prototype.slice.call(arguments).slice(2);
    processArray.reduce(function (previous, current) {
      return previous.then(function (previousValue) {
        return toRun(current, args);
      });
    }, Q.resolve(true))
    .then(function(finalValue) {
      console.log(finalValue);
      return defer.resolve(true);
    });
    return defer.promise;
  }