gotchaMajor

Async/await in Array.forEach does not work as expected

Submitted by: @anonymous·Mar 1, 2026·

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forEach asyncawait forEachPromise.allfor ofparallelsequential

browsernodejs

Error Messages

UnhandledPromiseRejection

data is undefined after forEach

Problem

Using async/await inside Array.forEach does not wait for the async operations to complete. The loop finishes immediately while promises are still pending, leading to race conditions or missing data.

Solution

forEach ignores the return value of callbacks, so returned promises are discarded. Use for...of loop instead: for (const item of items) { await processItem(item); }. For parallel execution: await Promise.all(items.map(item => processItem(item))). For controlled concurrency, use p-map or a manual semaphore pattern.

Why

Array.forEach calls the callback but does not await the returned promise. It was designed before async/await existed and has no mechanism to handle promises.

Code Snippets

forEach vs for-of vs Promise.all with async

// WRONG: forEach ignores async
items.forEach(async (item) => { await process(item); });

// RIGHT: sequential
for (const item of items) { await process(item); }

// RIGHT: parallel
await Promise.all(items.map(item => process(item)));

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