promised.js

MultiInstaller.prototype.forEach = function (visitor, callback) {
  var qVisitor = Q.nfbind(visitor, null)
    , qInstall = Q.nfbind(install)
    ;

  var target = this.target;
  var prefix = this.prefix;

  function process(versions, index, result) {
    if (!versions[index]) return result;

    return qInstall(target, versions[index], prefix)
             .then(function (result) { return qVisitor(result); })
             .then(process.bind(null, versions, ++index));
  }

  function installAll(versions) {
    console.log('installing all versions');
    return process(versions.reverse(), 0, null);
  }

  return this.versions().then(installAll).nodeify(callback);
};

In version I've done initially I'm not sure why I didn't use reduce right from beginning, with that, it goes down to three lines of code: https://gist.github.com/medikoo/4737974