Promise.all find which promise rejected

Question

In my code, I am using Promise.all() to run code asynchronously once some promises have all fulfilled. Sometimes, one promise will fail, and I\'m not sure why.

Answer 1

You can use an onreject handler on each promise:

Promise.all(promises.map((promise, i) =>
    promise.catch(err => {
        err.index = i;
        throw err;
    });
)).then(results => {
    console.log("everything worked fine, I got ", results);
}, err => {
    console.error("promise No "+err.index+" failed with ", err);
});

In general, every rejection reason should contain enough information to identify the issue that you need to handle (or log).