javascript - Make asyncawait loop execute in order - Stack Overflow

admin管理员组

文章数量:1344067

I have a loop that looks like that:

    newThreadIds.map(async function(id) {
      let thread = await API.getThread(id);
      await ActiveThread.findOneAndUpdate({number: id}, {posts: thread.posts}, {upsert: true}).exec();
      await Q.delay(1000);
    });

The problem is that each iteration executes asynchronously and I would like there to be a 1 second delay between them. I know how to do it with promises, but it looks ugly and I would prefer to do it with async/await and as little nesting as possible.

I have a loop that looks like that:

    newThreadIds.map(async function(id) {
      let thread = await API.getThread(id);
      await ActiveThread.findOneAndUpdate({number: id}, {posts: thread.posts}, {upsert: true}).exec();
      await Q.delay(1000);
    });

The problem is that each iteration executes asynchronously and I would like there to be a 1 second delay between them. I know how to do it with promises, but it looks ugly and I would prefer to do it with async/await and as little nesting as possible.

• javascript
• node.js
• async-await
• ecmascript-next

Share Improve this question Follow edited Feb 7, 2017 at 16:46 Victor Marchuk asked Feb 25, 2016 at 16:10 Victor MarchukVictor Marchuk 13.9k1212 gold badges4545 silver badges6767 bronze badges

Add a ment  | 

2 Answers 2

Sorted by: Reset to default 7

The map function doesn't know that its callback is asynchronous and returns a promise. It just runs through the array immediately and creates an array of promises. You would use it like

const promises = newThreadIds.map(async function(id) {
    const thread = await API.getThread(id);
    return ActiveThread.findOneAndUpdate({number: id}, {posts: thread.posts}, {upsert: true}).exec();
});
const results = await Promise.all(promises);
await Q.delay(1000);

For sequential execution, you would need to use Bluebird's mapSeries function (or something similar from your respective library) instead, which cares about the promise return values of each iteration.

In pure ES6, you'd have to use an actual loop, whose control flow will respect the await keyword in the loop body:

let results = [];
for (const id of newThreadIds) {
    const thread = await API.getThread(id);
    results.push(await ActiveThread.findOneAndUpdate({number: id}, {posts: thread.posts}, {upsert: true}).exec());
    await Q.delay(1000);
}

I've figured it out:

    for (let id of newThreadIds) {
      let thread = await API.getThread(id);
      await ActiveThread.findOneAndUpdate({number: id}, {posts: thread.posts}, {upsert: true}).exec();
      await Q.delay(1000);
    }

It's probably the best way to it with ES2015 and async/await.

本文标签： javascriptMake asyncawait loop execute in orderStack Overflow