How do you run promises in parallel in JavaScript?

Use a manual counter: track how many tasks have completed, store results in order, and call the final callback when all are done. This is verbose and error-prone. Use Promise.all instead for a cleaner solution.

Promise.all rejects if any promise rejects (fast fail). Promise.allSettled waits for all promises, even if some reject, and returns an array of { status, value/reason } objects. Use allSettled when you want all results regardless of failures.

Yes. The results array is in the same order as the input promises, regardless of which promise resolves first. This is one advantage over the manual counter approach with callbacks.