I have a function I use in my gulp setup that looks something like:

// browserified - the result of browserify(...)
x = function(browserified, entryScriptPath){
  // Promise is bluebird
  return new Promise(function(resolve, reject){
    var basename = path.basename(entryScriptPath, path.extname(entryScriptPath)) + '.js';
    browserified.bundle()
      .pipe(source(basename)) // vinyl-source-stream
      .pipe(buffer()) // vinyl-buffer
      .pipe(aGulpPlugin())
      .pipe(anotherGulpPlugin())
      //...
      .on('error', reject)
      .on('finish', resolve);
  });
}

An error was occurring while bundling but I got no textual error or stackerror, it just exited eventually with the wrong code. So I found this:

Return a readable stream with the javascript file contents or optionally specify a cb(err, buf) to get the buffered results.

I passed a callback like browserified.bundle(function(err){ if(err) reject(err); }) which worked fine when there was an error but that now breaks everything else when there isn't an error because the docs say you can either get a stream or a buffer but not both.

Is there a way I can grab this error another way and still keep my code? Or if not, I know I could move a lot of my stream stuff inside that callback but sorry I'm no stream expert and am unsure how to get that buffer into a vinyl transform stream which suits the gulp plugins. Like:

browserified.bundle(function(err, buf){
  if(err) return reject(err);

 // ????
 // something with buf
 // ????
 .pipe(aGulpPlugin())
 .pipe(anotherGulpPlugin())
 // ...
});