I am trying to figure out the best way to wait on the results of a subscription where I am passing in a callback. For example let's say I have the following:
function someMethod() {
let someResult = null;
someSubPub.subscribe(someTopic, someKey, someValue, (someResponse) => {
someResult = //do stuff in the callback with someResponse
});
return someResult;
}
I'm not quite sure how await would correctly work in this situation, aka blocking inside a callback.
Async/Await are nice, but sometimes it's simpler to think about the Promise construct that async/await abstracts away.
I suggest:
function someMethod() {
return new Promise((resolve, reject) => {
someSubPub.subscribe(someTopic, someKey, someValue, () => {
const someResult = //do stuff in the callback
resolve(someResult);
});
});
}
If you don't want to work with promises directly, you can wrap someSubPub.subscribe to return a promise
function someSubPubSubscribePromise(topic, key, value) {
return new Promise((resolve, reject) => {
someSubPub.subscribe(topic, key, value, resolve);
});
}
async function someMethod() {
await someSubPubSubscribePromise(someTopic, someKey, someValue);
const someResult = //do stuff in the callback
return someResult;
}
In either of those examples, you can do const result = await someMethod() (you can await both async methods and regular methods that return a promise)
One thing to consider: usually a pub/sub interface can call the callback multiple times. An async method / a method returning a promise can only resolve or reject exactly once. Probably you should be unsubscribing in the callback after you've responded to the event once?
