Node Async/Await Recursive Function ends code execution

Question

I have an issue with Node Async Await and recursive functions. For some reason, the code execution stops after resolving the Promise for a recursive function. Below is just a simple example I put in to demonstrate my issue (though found the problem while sending some requests with requests library).

If you run the code, you will see

Starting
Inside Promise

but not "Test Completed".

function promiseFunc(number) {
    return new Promise((resolve, reject) => {
        if (number == 100) {
            console.log('Inside Promise');
            resolve('Done');
        } else {
            number += 1
            promiseFunc(number);
        }
    })
}


(async function testFunc() {
    console.log('Starting');
    await promiseFunc(0)
    console.log("Test completed");
})()

Could someone please advise what is the issue?

Thank you in advance.

A new Promise() runs 101 times, a resolve() runs once. See the problem? — Ry-
– Ry- ♦, Commented Nov 6, 2019 at 11:18
Hmm..makes sense. Would you be able to help me convert my example to a right approach? Or at least point me to the right direction? — Constantin Suiu
– Constantin Suiu, Commented Nov 6, 2019 at 11:27
I do recommend you to read this article Promise Antipatterns You are probably having "The Collection Kerfuffle" ;) — Yury Tarabanko
– Yury Tarabanko, Commented Nov 6, 2019 at 11:31

Tudor Constantin · Accepted Answer · 2019-11-06 11:37:24Z

Here are some ways to fix it:

function promiseFunc(number) {
    return new Promise((resolve, reject) => {
        if (number == 100) {
            console.log('Inside Promise');
            resolve('Done');
        } else {
            number += 1;
            resolve(promiseFunc(number));
        }
    })
}


(async function testFunc() {
    console.log('Starting');
    await promiseFunc(0)
    console.log("Test completed");
})()

Or, interestingly enough, the equivalent code that uses async/await instead of explicit new Promise(...), works for your case:

// an async function returns a Promise
async function promiseFunc(number) {
        if (number == 100) {
            console.log('Inside Promise');
            return 'Done';
        } else {
            number += 1;
            // it seems to work as intended without saying return promiseFunc(...)
            promiseFunc(number);
        }
    }


(async function testFunc() {
    console.log('Starting');
    await promiseFunc(0)
    console.log("Test completed");
})()

Ankur Patel · Accepted Answer · 2019-11-06 11:35:39Z

-1

You have to do like this

  function promiseFunc(number) {
    return new Promise((resolve, reject) => {
        http.post('/api')
        .then((data) => {
            resolve(data);
        })
    })
}

    (async function testFunc() {
    console.log('Starting');
    const result = [];
    for (let index = 0; index < 100; index++) {
        result[index] = await promiseFunc(0);
    }
    console.log("Test completed");
})()

edited Nov 6, 2019 at 11:35

answered Nov 6, 2019 at 11:24

Ankur Patel

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2 Comments

Constantin Suiu Over a year ago

This was just an example to show my issue. The real life scenario I have is where I make an API call multiple times to wait for the needed response from the API, and then use the response further in the code.

Ankur Patel Over a year ago

Updated answer accoding to your requirement

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