Implement Promise.all from scratch

Easy20 minFree, no account

Ten lines, and three edge cases that separate a memorised answer from an understood one.

The question

Implement promiseAll(values) with the same semantics as Promise.all.

Then say how allSettled, race and any differ, and implement one of them.

promiseAll([p1, p2, p3]).then(([a, b, c]) => ...)

promiseAll([])            // resolves immediately with []
promiseAll([1, p, "x"])   // non-promises pass straight through
// rejects with the FIRST rejection, immediately

20:00Commit to an answer before you open the solution. Reading it first teaches you to recognise good answers, which is not the skill being tested.

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The worked solution

written by a person · not a grade

Score yourself

0 of 5 marked

Results in input order, written by index25
Explicit counter rather than inferring from the array25
Empty input resolves immediately20
Non-promise values handled15
Explained the family and what happens after a rejection15

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