如何定期调用生成器(异步)函数

本文介绍了如何定期调用生成器(异步)函数的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！ 问题描述

我正在构建一个必须每2秒轮询一次远程设备(生成器fn sendRequests())的应用.

I am building an app that must poll remote devices (generator fn sendRequests()) every 2 seconds.

使用setInterval调用生成器fn的正确方法是什么，它不是生成器，也不产生结果

What's the right way to call the generator fn using setInterval, which isn't a generator and doesn't yield

function * sendRequests() { // multiple remote async requests are sent } var timer = setInterval(() => { // yield sendRequests() }, 2000)

推荐答案

从 setInterval 回调产生的问题是 yield 只能屈服于生成器功能* 立即包含它.因此，您无法从回调中 yield .

The problem with yielding from the setInterval callback is that yield can only yield to the generator function* that immediately contains it. Therefore, you can't yield from a callback.

您可以通过回调来解决一个Promise，您的生成器函数可以对该Promise进行 yield :

What you can do from a callback is resolve a Promise, which your generator function can yield:

async function* pollGen() { yield new Promise((resolve, reject) => { setInterval(() => resolve(...), 2000); });

问题在于承诺只能解决一次.因此，每隔2000ms调用一次 resolve 将不会执行任何操作.

The problem with that is a Promise can only be settled once. Therefore, calling resolve every 2000ms won't do anything beyond the first call.

相反，您可以做的是在while循环中重复调用 setTimeout :

What you can do instead is call setTimeout repeatedly, in a while loop:

async function* pollGen() { let i = 0; while (i < 10) yield new Promise((resolve, reject) => { setTimeout(() => resolve(i++), 200); }); } (async function main() { // for-await-of syntax for await (const result of pollGen()) console.log(result); }());

新的 for-await-of 语法自Node v9.2起可用，并且可以在Nodev10或更高版本中使用而没有任何标志.

The new for-await-of syntax has been available since Node v9.2, and can be used in Nodev10 or later without any flags.