Promise.allSettled()
The Promise.allSettled()
method returns a promise that
resolves after all of the given promises have either fulfilled or rejected, with an
array of objects that each describes the outcome of each promise.
It is typically used when you have multiple asynchronous tasks that are not dependent on one another to complete successfully, or you'd always like to know the result of each promise.
In comparison, the Promise returned by Promise.all()
may be more
appropriate if the tasks are dependent on each other / if you'd like to immediately
reject upon any of them rejecting.
Syntax
Promise.allSettled(iterable);
Parameters
Return value
A pending Promise
that will be
asynchronously fulfilled once every promise in the specified collection
of promises has completed, either by successfully being fulfilled or by being rejected.
At that time, the returned promise's handler is passed as input an array containing the
outcome of each promise in the original set of promises.
However, if and only if an empty iterable is passed as an argument,
Promise.allSettled()
returns a Promise
object that has
already been resolved as an empty array.
For each outcome object, a status
string is present. If the status is
fulfilled
, then a value
is present. If the status is
rejected
, then a reason
is present. The value (or reason)
reflects what value each promise was fulfilled (or rejected) with.
Examples
Using Promise.allSettled
Promise.prototype.then()
Promise.allSettled([
Promise.resolve(33),
new Promise(resolve => setTimeout(() => resolve(66), 0)),
99,
Promise.reject(new Error('an error'))
])
.then(values => console.log(values));
// [
// {status: "fulfilled", value: 33},
// {status: "fulfilled", value: 66},
// {status: "fulfilled", value: 99},
// {status: "rejected", reason: Error: an error}
// ]
await
const values = await Promise.allSettled([
Promise.resolve(33),
new Promise(resolve => setTimeout(() => resolve(66), 0)),
99,
Promise.reject(new Error('an error'))
])
console.log(values)
// [
// {status: "fulfilled", value: 33},
// {status: "fulfilled", value: 66},
// {status: "fulfilled", value: 99},
// {status: "rejected", reason: Error: an error}
// ]
Specifications
Specification |
---|
ECMAScript Language Specification # sec-promise.allsettled |
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