Dealing with errors in Promise.all

promise_all_errors.md

Dealing with errors in Promise.all

Promise.all stops execution if any of the Promises have an uncaught error.

async function wait(ms) {
    return new Promise((resolve) => {
        setTimeout(resolve, ms);
    });
}

const p1 = new Promise(
    async (resolve, reject) => {
        await wait(1000);
        resolve(1);
    }
)

const p2 = new Promise(
    async (resolve, reject) => {
        reject(new Error("noooooo"));
    }
)

// will stop when p2 rejects
await Promise.all([p1, p2]).then(result => console.log(result))  // result: undefined

In order to allow the execution of the other promises to continue, you have to catch the errors and deal with them.

async function wait(ms) {
    return new Promise((resolve) => {
        setTimeout(resolve, ms);
    });
}

function logError(err) {
    return console.error(err)
}

const p1 = new Promise(
    async (resolve, reject) => {
        await wait(1000);
        resolve(1);
    }
).catch(logError);  // catch the error

const p2 = new Promise(
    async (resolve, reject) => {
        reject(new Error("noooooo"));
    }
).catch(logError);  // gotta catch 'em all

// will log the error in p2 and then wait for p1 to finish
await Promise.all([p1, p2]).then(result => console.log(result))  // result: [1, undefined]