old_contents: import { Tracker } from 'meteor/tracker';
  
  const getTrackerLoader = reactiveMapper => (
    (props, onData, env) => {
      let trackerCleanup = null;
  
      const handler = Tracker.nonreactive(() =>
        Tracker.autorun(() => {
          trackerCleanup = reactiveMapper(props, onData, env);
        }),
      );
  
      return () => {
        if (typeof trackerCleanup === 'function') trackerCleanup();
        return handler.stop();
      };
    }
  );
  
  export default getTrackerLoader;
  
  
new_contents: import { Tracker } from 'meteor/tracker';
  
  const getTrackerLoader = reactiveMapper => (
    (props, onData, env) => {
      let trackerCleanup = null;
  
      const handler = Tracker.nonreactive(() =>
        Tracker.autorun(() => {
          trackerCleanup = reactiveMapper(props, onData, env);
        })
      );
  
      return () => {
        if (typeof trackerCleanup === 'function') trackerCleanup();
        return handler.stop();
      };
    }
  );
  
  export default getTrackerLoader;
  
subject: Clean code