当被调用时,则只要 Immediate 处于活动状态,就会要求 Node.js 事件循环不要退出。 多次调用 immediate.ref() 没有影响。

默认情况下,所有的 Immediate 对象都是 ref 的,通常不需要调用 immediate.ref(),除非之前调用了 immediate.unref()

When called, requests that the Node.js event loop not exit so long as the Immediate is active. Calling immediate.ref() multiple times will have no effect.

By default, all Immediate objects are "ref'ed", making it normally unnecessary to call immediate.ref() unless immediate.unref() had been called previously.