Promises run linearly.

xmpl.js

  visitAll : function (prefix, target, visitor) {
    /* Installs and visits must happen sequentially so node_modules doesn't
     * get stomped mid-run.
     */
    function installAndVisit(versions, index, result) {
      if (!versions[index]) return result;

      return installer.visitVersion(prefix, target, versions[index], visitor)
               .then(installAndVisit.bind(null, versions, index - 1));
    }

    function installAll(versions) {
      console.log("Installing %s versions of %s.", versions.length, target);

      recreate(prefix, 'build-errors');

      return installAndVisit(versions, versions.length - 1);
    }

    return installer.versions(target).then(installAll);
  }