Most of the time, there is no observable difference between return and return await. Both versions of delay1Second have the exact same observable behavior (but depending on the implementation, the return await version might use slightly more memory because an intermediate Promise object might be created).
However, as @PitaJ pointed out, there is one case where there is a difference: if the return or return await is nested in a try–catch block. Consider this example
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 the first version, the async function awaits the rejected promise before returning its result, which causes the rejection to be turned into an exception and the catch clause to be reached; the function will thus return a promise resolving to the string “Saved!”.
The second version of the function, however, does return the rejected promise directly without awaiting it within the async function, which means that the catch case is not called and the caller gets the rejection instead.