* [Promise.race Example](./docs/Closures/Promise.race.md)

[Details](https://github.com/nodejs/node/issues/17469#issuecomment-685216777)

When you call Promise.race with a long-running promise, the resolved value of the returned promise gets retained for as long as each of its promises do not settle.

Example code to demonstrate:

async function randomString(length) {

await new Promise((resolve) => setTimeout(resolve, 1));

let result = "";

const characters = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789";

for (let i = 0; i < length; i++) {

result += characters.charAt(Math.floor(Math.random() * characters.length));

}

return result;

}

(async function main() {

let i = 0;

const pending = new Promise(() => {});

while (true) {

await Promise.race([pending, randomString(10000)]);

if (i++ % 1000 === 0) {

const usage = process.memoryUsage();

const rss = Math.round(usage.rss / (1024 ** 2) * 100) / 100;

const heapUsed = Math.round(usage.heapUsed / (1024 ** 2) * 100) / 100;

console.log(`RSS: ${rss} MiB, Heap Used: ${heapUsed} MiB`);

}

}

})();

In this example, we pass a large random string along with a non-settling promise to Promise.race, and the result is that every single one of these strings is retained.

**How to fix:**

Avoid Promise.race. Replacing your "await Promise.race" expressions with "await new Promise" expressions, where the newly constructed Promise sets a function variable in the outer scope.

(async function main() {

let i = 0;

// These functions are set in a promise constructor later

let resolve;

let reject;

const pending = new Promise(() => {});

pending.then((value) => resolve(value), (err) => reject(err));

while (true) {

randomString(10000).then((value) => resolve(value), (err) => reject(err));

// This is the await call which replaces the `await Promise.race` expression in the leaking example.

// It sets callbacks for our promises

await new Promise((resolve1, reject1) => {

resolve = resolve1;

reject = reject1;

});

if (i++ % 1000 === 0) {

const usage = process.memoryUsage();

const rss = Math.round(usage.rss / (1024 ** 2) * 100) / 100;

const heapUsed = Math.round(usage.heapUsed / (1024 ** 2) * 100) / 100;

console.log(`RSS: ${rss} MiB, Heap Used: ${heapUsed} MiB`);

}

}

})();

* [Promise.race Example](./Promise.race.md)