Promise.allSettled: Examples and Use Cases in JavaScript

Promise.allSettled: Examples and Use Cases in JavaScript

Promise.allSettled waits for all promises to settle, even if some reject. Here are practical examples.

Basic Usage

const results = await Promise.allSettled([
  fetchA(),
  fetchB(),
  fetchC(),
]);
results.forEach((r) => {
  if (r.status === "fulfilled") {
    console.log("Success:", r.value);
  } else {
    console.error("Failed:", r.reason);
  }
});
``
Each result has a `status` (`"fulfilled"` or `"rejected"`). Fulfilled results have `value`; rejected results have `reason`.

### Partial Success

```js
const results = await Promise.allSettled([
  fetchUser(1),
  fetchUser(2),
  fetchUser(3), // this one fails
]);
const successful = results.filter((r) => r.status === "fulfilled").map((r) => r.value);
const failed = results.filter((r) => r.status === "rejected").map((r) => r.reason);
console.log("Successful:", successful);
console.log("Failed:", failed);
``
You get all successful results and all failures. No fast fail.

### Fetching from Multiple Sources (Best Effort)

```js
const results = await Promise.allSettled([
  fetchFromCache(),
  fetchFromCDN(),
  fetchFromOrigin(),
]);
const firstSuccess = results.find((r) => r.status === "fulfilled");
if (firstSuccess) {
  render(firstSuccess.value);
}
``
Try multiple sources and use the first successful one (or all successful ones).

### Difference from Promise.all

```js
// Promise.all: fast fail (if any rejects, the whole thing rejects)
const [a, b, c] = await Promise.all([fetchA(), fetchB(), fetchC()]);

// Promise.allSettled: wait for all (never rejects)
const results = await Promise.allSettled([fetchA(), fetchB(), fetchC()]);
``
### The Takeaway

`Promise.allSettled` waits for all promises, even if some reject. Each result has `{ status, value/reason }`. Use for partial success (some results even if some fail), best-effort fetching from multiple sources, and when you never want the whole thing to reject. Never fast-fails.