allSettled

allSettled is a static method on the JavaScript Promise object. It is defined as Promise.allSettled(iterable) and returns a new Promise that resolves after all of the input promises have settled, meaning they have either fulfilled or rejected. The resolved value is an array describing the outcome of each input, in the same order as the input iterable.

The result array contains objects with a uniform shape. For a fulfilled input, the corresponding element is { status: 'fulfilled', value: ... }. For a rejected input, the element is { status: 'rejected', reason: ... }. If an input is not a promise, it is treated as a fulfilled value and included as { status: 'fulfilled', value: ... }. The method does not short-circuit on rejection, so it waits for all inputs to settle.

Syntax and behavior notes: allSettled accepts any iterable of promises or values and returns a promise that resolves to the array of outcome objects when all have settled. If the iterable is empty, it resolves immediately to an empty array. Unlike Promise.all, allSettled never rejects; it always resolves with the outcomes of all inputs.

Example:

const promises = [

Promise.resolve(1),

Promise.reject(new Error('boom')),

3

];

Promise.allSettled(promises).then(results => console.log(results));

// [{ status: 'fulfilled', value: 1 }, { status: 'rejected', reason: Error('boom') }, { status: 'fulfilled', value: 3 }]

History and compatibility: allSettled was introduced in ECMAScript 2020 (ES11). It is supported in modern browsers and Node.js (around Node 12 onward). Polyfills are available for older environments. Use allSettled when you need a complete picture of multiple asynchronous operations, regardless of whether some fail. See also Promise.all, Promise.any, and Promise.race for alternative aggregation patterns.