Is it possible to wrap a setInterval in an async generator function?

Question

Without using the Streams API, is it possible to wrap a setInterval in an async generator function, to simulate a never-ending stream?

I know how to do it using setTimeout to supply the delay.

Using setTimeout:

const wait = (delay = 500) => new Promise((resolve) => setTimeout(resolve, delay))

async function * countUp(count = 0) {           
    while(1) (await wait(), yield count++)           
}

(async ()=> {
    for await(let el of countUp())
        console.log(el)
})()

You could, but I don't think it would be as tidy as using setTimeout as a promise delay. — Keith, Mar 10 '20 at 18:48
@52d6c6af fair enough, i guess your question is an exception to the rule. — r3wt, Mar 11 '20 at 21:17

Bergi · Accepted Answer · 2020-03-10T19:23:56.547

1

No. Or: not easily. Async generator functions are promise based, and promises don't deal well with repetitive callbacks. Also setInterval does not support any form of backpressure.

Of course you can implement the streams API yourself, which comes down to making a queue of promises. You can take the code from that answer and write

function countUp(count = 0) {
    const q = new AsyncBlockingQueue()
    setInterval(() => {
        q.enqueue(count++)
    }, 500)
    return q // has a Symbol.asyncIterator method
}

(async() => {
    for await (const el of countUp())
        console.log(el)
})()

edited Mar 10 '20 at 19:23

answered Mar 10 '20 at 19:08

Bergi

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So the answer is actually "yes", but it is much more difficult? – Ben Aston Mar 11 '20 at 12:35
Not just more difficult, but also more inefficient and possibly incorrect if the consumer doesn't keep up with the rate of production – Bergi Mar 11 '20 at 13:22

Is it possible to wrap a setInterval in an async generator function?

1 Answers1