This is possibly a code style related question, I studied a little deeper so
this is how I currently learned:
If you want a special Promise (subclass or extended), you should not use async
function since it casts the return value to a standard Promise
If you want to return a promise and attach callbacks to it (not returning
promise that spawns by then), you should not use async
function foo() {
var waiting = fetchResource();
// Since this code you should not use async functions
waiting.then(logMessage);
return waiting;
}
After all above cases, it is still OK to use none async functions that returns
Promise, but it’s quite hard to determines if one method is actual async (with
Promise) or sync (immediately return values), so I may preferr to mark all
async function async for better read experience
Never write return await xxx;, it seems useless either xxx is a promise or not
Anyway this is not an issue about spec itself, it’s more like an open
discussion, thanks for reply :)
Best regards
Gray Zhang
在 2015年6月3日 下午4:18:14, Gruenaum Benjamin ([email protected]) 写到:
A function needs to be defined `async` if you intend to possibly use the await
keyword inside it.
> If a function is returning Promise, it MUST be async If a function depends on
> an async function, it **MUST be async A further question could be, if one
> function only contains some simple then calls to promise, should it become an
> async function and use await in all possible cases to eliminate then calls?
No, it's possible to have legitimate use cases where this is not the case, for
example:
```js
async function foo() { ...} // queries an API
async function bar() { ... } // queries an API
function fooBar() {
return Promise.all([foo(), bar()]);
}
```
It's a contrived simplified example but the point is you might have functions
that work on promises that should not themselves be `async`.
For example, in your updateUser function, you can remove `async` and `await`
and get the same value (as you observed in growUp1).
To clarify, there is no _semantic_ distinction in your examples between an
async function and a regular function that returns a promise - it's just syntax
sugar - just like generators and regular functions that return iterables.
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