watcher.ref()
- 返回: <fs.FSWatcher>
调用时，只要 FSWatcher 处于活动状态，就请求 Node.js 事件循环不退出。
多次调用 watcher.ref() 将不起作用。
默认情况下，所有 FSWatcher 对象都被“引用”，这使得通常不需要调用 watcher.ref() 除非之前已经调用过 watcher.unref()。
- Returns: <fs.FSWatcher>
When called, requests that the Node.js event loop not exit so long as the
FSWatcher is active. Calling watcher.ref() multiple times will have
no effect.
By default, all FSWatcher objects are "ref'ed", making it normally
unnecessary to call watcher.ref() unless watcher.unref() had been
called previously.
