Difference between Promise.all and Promise.allSettled?

Promise.all rejects as soon as any input promise rejects and discards the other results, so it is all-or-nothing. Promise.allSettled never rejects; it waits for every promise and returns an array of objects each describing fulfilled with a value or rejected with a reason. Use allSettled when partial failures are acceptable.

Difference between Promise.any and Promise.race?

Promise.race settles with the first promise to settle, whether it fulfills or rejects. Promise.any ignores rejections and fulfills with the first fulfillment, only rejecting with an AggregateError if every promise rejects. Use any when you want the first success and race when you want the first result of any kind.

What does Promise.resolve do with a promise?

Promise.resolve(value) returns a promise fulfilled with value, but if value is already a thenable it returns that same promise rather than wrapping it. This makes it safe to normalize a value that may or may not already be a promise before awaiting it.

How does finally differ from then?

finally runs a callback when the promise settles either way and, crucially, passes the original fulfillment value or rejection reason straight through. It takes no arguments and is for cleanup like hiding a spinner. then receives the value and can transform it.

What is Promise.withResolvers?

Promise.withResolvers() returns an object with a new promise plus its resolve and reject functions, so you can settle the promise from outside its executor. It replaces the older pattern of declaring resolve and reject variables and assigning them inside a new Promise constructor.

JavaScript Promise API Reference

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The Promise API is small but each combinator has a precise rule for when it fulfills and when it rejects, and choosing the wrong one causes silent data loss or unhandled rejections. This reference lists every Promise method with its settlement rule and the equivalent async/await pattern.

How it works

A Promise is in one of three states: pending, fulfilled, or rejected. Instance methods register callbacks:

then(onFulfilled, onRejected) transforms the value or handles rejection.
catch(onRejected) is shorthand for then(undefined, onRejected).
finally(onFinally) runs on either outcome and passes the result through.

The static combinators take an iterable of promises and differ only in their settlement rule:

Promise.all        // fulfills with all values; rejects on first rejection
Promise.allSettled // never rejects; array of {status, value|reason}
Promise.any        // first fulfillment; AggregateError if all reject
Promise.race       // first to settle, fulfill OR reject, wins

Tips

Use all when you need every result and any failure should abort the batch; use allSettled when partial failure is fine and you want to inspect each outcome. Reach for any to get the first success across redundant sources, and race to enforce a timeout (Promise.race([work, timeout])). Always attach a catch or await inside try/catch — an unhandled rejection crashes Node and logs a warning in browsers.