NodeJS - Wait for return inside setTimeout

Question

I am trying to learn async/await. I want to wait for the return statement inside my async function. I have to call it several times so I used a setTiemout inside.

EDIT:

//Processing gallery
async function somefunction(){
    async function getPictureR(){

        /* some code */

        if($('.actions > .prev', html)[0]){
            older = $('.actions > .prev', html)[0].attribs.href;
        } else {
            console.log('return');
            return;
        }

        /* some code */

        return new Promise((resolve, reject) => {
            setTimeout(getPictureR, 1 * 1000/2);    
        })
    }
    await getPictureR();
    console.log('getPictureR done');
}

I've tried await getPictureR() but it triggers right after the first call to the function. How can I wait for that return ?

You need to promisify `setTimeout`. Then you can just `await` it in a loop. — Bergi, Dec 09 '18 at 13:24
Could you elaborate please ? I've just read the nodejs documntation but I don't get it. The example executes the code after the first setTimeout call — Badong, Dec 09 '18 at 13:35
@Bergi Looks like I've commented a bit fast. Can you still help ? — Badong, Dec 09 '18 at 14:17
Can you [edit] the question to show what you tried? Maybe you were on the right path. — Bergi, Dec 09 '18 at 14:18
just did. I thought this would work, but now the code after `getPictureR()` isn't executed — Badong, Dec 09 '18 at 14:25

Bergi · Accepted Answer · 2018-12-09T14:40:25.867

You should never call a promise-returning function, like getPictureR, from an asynchronous (non-promise) callback or inside the new Promise constructor. You also were never resolving the new Promise. You are looking for

return new Promise((resolve, reject) => {
    setTimeout(resolve, 1 * 1000/2);    
}).then(() => {
    return getPictureR(); // do the promise call in a `then` callback to properly chain it
})

But since you're using async/await, you don't need the recursive function and the then chaining anyway. Also you can factor out the setTimeout-in-promise wrapping in a separate helper function:

function delay(t) {
    return new Promise(resolve => setTimeout(resolve, t));
}
async function somefunction() {
    while (true)
        /* some code */

        const prev = $('.actions > .prev', html);
        if (prev.length) {
            older = prev[0].attribs.href;
        } else {
            console.log('return');
            break;
        }

        /* some code */

        await delay(1 * 1000/2);
//      ^^^^^^^^^^^
    }
    console.log('getPicture done');
}

This works like a charm ! I would have never thought of using a `while` loop, Thanks again ! — Badong, Dec 09 '18 at 15:01

NodeJS - Wait for return inside setTimeout

1 Answers1