How to Return the Response from an Asynchronous Call (Without Losing It)

Title

How to Return the Response from an Asynchronous Call (Without Losing It)

Alternate Title Options

Async Return Values: Why You Keep Getting Undefined and How to Fix It

Await or Else: Returning Data from Async Functions the Right Way

Promises, Callbacks, and Real Results: The Async Return Fix

Meta Description (155-160 chars)

Fix async return bugs with await patterns, promise chaining, and debugging checks so JavaScript or TypeScript functions return real data on time in production.

Assumptions

Reader: web developers (junior to mid) working in JavaScript or TypeScript.

Goal: return data reliably from async functions and stop undefined results.

Context: browsers, Node.js, and HTTP APIs.

Angle: async bugs are timing bugs; make the timing explicit.

Length: ~1800-2200 words.

Format: Blog.

SEO keyword: return response from async call. Related terms: async await return value, promise return undefined, callback return value, JavaScript async function, TypeScript async await.

Constraints: no framework lock-in, no hype.

1) Hook: the scene + the pain

It is 6:12 PM and you are supposed to be done.

You log the API response inside a promise and see the right data.

Then your function returns undefined to the caller.

You add more console logs, more then blocks, and more confusion.

A teammate says, "Just set a timeout." You do, and it still fails.

Here is what is actually happening and how to fix it.

Three things people say out loud:

"But I returned it inside the callback."

"The console shows the data, why is my variable empty?"

"It works in one place and breaks in another."

> If you only remember one thing: You cannot return from the future. Await it or return a promise.

2) The real problem (plain English)

Your code executes in two timelines: now and later. Async work happens later, but your function returns now. That is why the return value is undefined even when the data exists.

The fix is not a hack. The fix is to make the timeline explicit so the caller knows when the data is ready.

3) What is going on under the hood (deeper, but still clear)

When you call an async function, it immediately returns a promise. The actual work continues in the background. If you return inside a callback, you only return from the callback, not from the outer function.

Promises are just contracts: "I will give you a value later." If the caller does not await that contract, they will read the value too early.

Think of it like ordering food at a counter. You get a ticket, not the meal. If you try to eat the ticket, you are going to be disappointed.

4) The fix (step-by-step)

Step 1: Decide what you want to return.

If the caller needs the data, return a promise or make the function async.

Step 2: Use await for async calls.

Make the async boundary visible and wait for the result before using it.

Step 3: Propagate the promise.

If you cannot use await, return the promise to the caller.

Step 4: Handle errors explicitly.

Use try/catch for await or a catch handler for promises.

Step 5: Validate with a minimal test.

Write a short test that asserts the returned value, not just a console log.

Quick win

Add await and return the awaited value.

Mark the function async so callers know it returns a promise.

Best practice

Keep async boundaries shallow and explicit.

Prefer async/await over nested callbacks.

Use typed return values (Promise) so TypeScript catches misuse.

> Pro tip: If you see undefined, trace where the promise was never awaited.

> Watch out: setTimeout is not a fix. It only hides the bug until timing changes.

5) Example(s) (code/commands/config) + explanation line-by-line

Example A: The common bug (returning inside a callback)

function getUserName(userId: string) {
  let name: string | undefined;

  fetch('/api/users/' + userId)
    .then((response) => response.json())
    .then((data) => {
      name = data.name;
      return name; // Returns from the callback, not getUserName
    });

  return name; // Returns before the fetch finishes
}

Explanation:

Line 1 starts a function that returns immediately.

Line 4 schedules work for later.

Line 7 returns from the inner callback only.

Line 10 returns before the network call finishes.

Example B: The correct async/await version

async function getUserName(userId: string): Promise<string> {
  const response = await fetch('/api/users/' + userId);
  if (!response.ok) {
    throw new Error('Request failed: ' + response.status);
  }

  const data = await response.json();
  return data.name ?? 'Unknown';
}

Explanation:

Line 1 makes the return type explicit.

Line 2 waits for the HTTP request to finish.

Line 3-5 fails fast on bad responses.

Line 7 waits for JSON parsing.

Line 8 returns a real value to the caller.

Example C: Returning the promise for callers that chain

function getUserName(userId: string): Promise<string> {
  return fetch('/api/users/' + userId)
    .then((response) => {
      if (!response.ok) {
        throw new Error('Request failed: ' + response.status);
      }
      return response.json();
    })
    .then((data) => data.name ?? 'Unknown');
}

Explanation:

Line 1 returns a promise immediately.

Line 2-7 keep error handling inside the chain.

Line 8 transforms the response into the final value.

6) Common pitfalls (and how to spot them fast)

Returning from a callback and expecting the outer function to return.

Logging the data and assuming it was returned.

Forgetting to await a promise in the caller.

Mixing callbacks, promises, and async/await in one function.

Debugging: symptoms -> likely causes -> checks

Returned value is undefined -> missing await -> check call sites for await.

Works in one place, fails in another -> caller not awaiting -> search for the function usage.

Caught in then, not in try/catch -> promise chain used without await -> confirm async boundary.

Random timing bugs -> setTimeout bandaid -> remove and await correctly.

7) Checklist / TL;DR (copyable)

- [ ] Decide if the function returns data or a promise.
- [ ] Add async and await the call.
- [ ] Return the awaited value.
- [ ] Propagate the promise if you cannot await.
- [ ] Handle errors explicitly.
- [ ] Validate with a small test.

8) Optional: When NOT to do this + alternatives

If a caller cannot be async (legacy APIs or sync-only hooks), return a promise and adapt at the boundary with a single wrapper function. Do not sprinkle timeouts everywhere.

If you need concurrency, use Promise.all and await once at the edge of your flow.

9) Best practices

Keep async boundaries minimal and obvious.

Prefer async/await for readability.

Use typed return values and avoid implicit any.

Centralize error handling in one place per flow.

10) Closing: what to do next

Pick one async function in your codebase and make its return type explicit. That single change usually reveals every call site that is returning too early.

Copy/paste checklist:

- [ ] Make the function async or return a promise.
- [ ] Await the async call.
- [ ] Return the awaited value.
- [ ] Test the returned data, not just logs.

Mini FAQ:

Q: Why does it log the right data but return undefined?

A: The log happens later, but the function returns now.

Q: Should I use callbacks or promises?

A: Prefer promises and async/await for clearer flow and error handling.

Q: Can I fix it with setTimeout?

A: No. That hides the timing bug and will fail under different conditions.

Q: How do I return multiple async results?

A: Use Promise.all and await the array of results.