How to call a generator (async) function on an interval basis

Question

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

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)

Answer 1

Since AdonisJS uses co() under the hood, I used @Bergi suggestion of wrapping in co()

function * sendRequests() {
  // multiple remote async requests are sent
}

var timer = setInterval(() => {
  co(function * () {
    yield sendRequests()
  })
}, 2000)

Answer 2

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.

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);
  });

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.

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); }()); 

The new for-await-of syntax has been available since Node v9.2, and can be used in Node v10 or later without any flags.