code: function bundleHandler (pathToHandlers, module, file) {
  
      // only rebundle if js file changed
      if (file.length < 3 || file.indexOf('bundle.') === 0 || file.substr(file.length - 3) !== '.js') {
          return;
      }
  
      // only rebundle if handler was already bundled before
      fs.access(pathToHandlers + '/bundle.' + file, err => {
  
          if (err && err.code === 'ENOENT') {
              return ;
          }
  
          let fnIri = module + '/' + file.slice(0, -3);
  
          // remove the old bundle
          fs.unlink(pathToHandlers + '/bundle.' + file, err => {
  
              if (err) {
                  console.log('Failed to delete old bundle for handler: ' + fnIri);
                  return console.log(err);
              }
  
              // build the new bundle
              console.log('Bundle handler: ' + fnIri);
              runtime.bundle(fnIri, {}, (err) => {
  
                  if (err) {
                      console.log('Failed to bundle handler: ' + fnIri);
                      return console.log(err);
                  }
  
                  console.log('Bundle done for handler: ' + fnIri);
              });
          });
      });
  }
docs: this will rebundle a handler