如何设置NodeJS在退出之前等待事件循环为空？

Question

I'm writing a simple JS file that executes a bunch of promises that I don't care to know their state. If I start node like this: node index.js node will exit as soon as it finished firing the promises, while they still are doing things in the background.

Is it possible to pass a parameter to node and tell it to wait until the event loop is empty before it exiting?

I did check node --help but did not find anything that could be the option that I'm looking for.

IMPORTANT: I'm not looking for a code solution, but a parameter to pass to node itself.

Answer 1

Is it possible to pass a parameter to node and tell it to wait until the event loop is empty before it exiting?

No, there is no such parameter. The desired behaviour is the default in node, it cannot be changed. Node does exit the event loop when the event queue is empty and there are no running asynchronous tasks.

Something is broken in the code if it is still doing things in the background but didn't register the task.

Answer 2

I don't think there is such a feature that you can make use of to achieve the expected result. But, if you want your node process to wait until the promises are finished you can await for them.

For any timers, nodejs provides ways to cancel them ( Doc ).

If you want to wait for your timers to execute then you can maintain a global variable to track states of a timer.

Answer 3

Your code needs to be doing something in order for node to keep running. One of the things it could be doing is simply waiting for other code to complete. There are many ways that can be done. A simple example might look something like this:

const resolveLater = () => {
  return new Promise(resolve => setTimeout(resolve, 5000));
}

resolveLater().then(() => console.log('Done'));

If you need multiple events, the easiest thing to do might be to do a single asynchronous function that waits for them all. Eg

const resolveLater = (delay) => {
  return new Promise(resolve => setTimeout(resolve, delay));
}

const resolveAll = async () => {
  await Promise.all([
    resolveLater(1000),
    resolveLater(2000),
    resolveLater(5000),
  ]);
}

resolveAll().then(() => console.log('Done'));

You don't have to do anything with the promises other than wait for them to complete . You do care about their state, even if you don't care about their results.