code: function gulpAngularJsx() {
  
      // creating a stream through which each file will pass
      var stream = through.obj(function(file, enc, cb) {
          if (file.isStream()) {
              this.emit('error', new PluginError(PLUGIN_NAME, 'Streams are not supported!'));
              return cb();
          }
  
          if (file.isBuffer()) {
              file.contents = new Buffer(angularjsx.convert(file.contents));
          }
  
          // make sure the file goes through the next gulp plugin
          this.push(file);
  
          // tell the stream engine that we are done with this file
          cb();
      });
  
      // returning the file stream
      return stream;
  }
docs: plugin level function (dealing with files)