Awaitable Differences: When Should You `return await promise` vs `return promise`?

Awaitable Differences: return await promise vs return promise

When using asynchronous functions, there are two variations commonly used: return await promise and return promise. While these may seem similar at first glance, there are subtle differences that can impact behavior.

Immediate Resolution vs Awaiting Resolution

The primary difference lies in the timing of promise resolution. In return await promise, the async function waits for the promise to resolve before returning its value. This means that the value returned by the function is the resolved value of the promise.

On the other hand, return promise returns the promise object itself without awaiting its resolution. This allows the caller to handle the promise resolution outside the async function.

Error Handling Within the Async Function

When using return await promise, any errors thrown by the promise will be caught within the async function and bubble up to the caller. This provides a way to handle errors within the same function that initiated the asynchronous operation.

In contrast, when using return promise, errors thrown by the promise will not be caught within the async function and will be propagated to the caller. This requires the caller to handle the errors externally.

Performance Considerations

While both methods have the same observable behavior, the use of return await may have a slightly higher memory footprint. This is because an intermediate Promise object may be created when using return await, which can consume additional memory.

Nested Try-Catch Blocks

The most significant difference between the two variations occurs when the return await or return statements are nested within try-catch blocks. In this case, return await ensures that the async function waits for the promise to resolve before the catch block is executed. This means that the catch block will only execute if an error occurs after the promise has resolved.

In contrast, with return (without await), the promise is returned immediately without awaiting its resolution. Therefore, if an error occurs before the promise resolves, the catch block will execute.

Conclusion

While return await promise and return promise generally have the same observable behavior, the choice between the two depends on the specific use case and error handling requirements. For error handling within the async function, return await promise is preferred. If the caller needs to handle the promise resolution externally or for performance considerations, return promise may be more appropriate.

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