Index in Promise.all

Question

The Promise.all method doesn't have an index to target a particular promise so in my case, I'm wondering if I can do this:

let promises = [Promise.resolve(true), 
                Promise.resolve(true), 
                Promise.resolve(false), 
                Promise.resolve(true)];

Promise.all(promises).then(result => {
    console.log(result);
    // [true, true, false, true]

    let failed = result.findIndex(r => !r);
    console.log(promises[failed]);

});

Now this is assuming the order is always maintained, i.e the result array is always in the same sequence as the input array?

Yes, the order will remains same in the same order you execute the promises — Shailesh Rathod, Jan 07 '19 at 05:47

score 2 · Accepted Answer · answered Jan 07 '19 at 05:47

2

When using Promise.all, the array returned will always be in the same order as the array provided, so you can safely use a set index.

answered Jan 07 '19 at 05:47

Icehorn

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How do you know? Is there an authoritative reference for this? – eozzy Jan 07 '19 at 05:51
1

The MDN web docs are a good source of information for these types of questions: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise/all – Icehorn Jan 07 '19 at 06:01

Index in Promise.all

1 Answers1