When should I use `return await promise` over `return promise` in JavaScript?

Return await Promise vs Return Promise

In JavaScript, the difference between return await promise and return promise in asynchronous functions is often subtle. However, there are certain scenarios where they exhibit distinct behaviors, as explored below:

Delays and Observability:

In the provided code examples, delay1Second functions using both approaches return Promises that resolve after a 1-second delay. Both versions appear to behave similarly in terms of observable results.

Error Handling:

Typically, both approaches do not impact error handling within the asynchronous function or the propagation of errors to the caller. In both cases, errors would bubble out of the function's Promise.

Memory Consumption:

Although not directly observable, the return await promise version may slightly increase memory consumption compared to the return promise approach. This is because an additional Promise object may be created and awaited during execution.

Try-Catch Blocks:

A subtle but important distinction arises when using these approaches within try-catch blocks. Consider the following examples:

async function rejectionWithReturnAwait() {
  try {
    return await Promise.reject(new Error());
  } catch (e) {
    return "Saved!";
  }
}

async function rejectionWithReturn() {
  try {
    return Promise.reject(new Error());
  } catch (e) {
    return "Saved!";
  }
}

In rejectionWithReturnAwait, the awaited rejection throws an exception, which is caught in the catch block. As a result, the function resolves to "Saved!".

Conversely, in rejectionWithReturn, the rejection is returned directly without awaiting within the async function. This means the catch block is not executed, and the caller receives the rejection instead.

Conclusion:

While the difference between return await promise and return promise is usually negligible, it's crucial to be aware of the potential implications when using try-catch blocks. In most cases, either approach can be used with minimal impact. However, for precise error handling within try-catch blocks, return await promise should be preferred to ensure that rejections are caught and handled correctly within the async function.

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