I am following apollo tutorials ( https://www.apollographql.com/docs/tutorial/resolvers/ ) and I saw this code:
me: async (_, __, { dataSources }) =>
dataSources.userAPI.findOrCreateUser()
Because dataSources.userAPI.findOrCreateUser()
returns Promise , I thought that await dataSources.userAPI.findOrCreateUser()
was right.
But it working really well without any errors and I got resolved value in React... even this below code working well too.
me: (_, __, { dataSources }) =>
dataSources.userAPI.findOrCreateUser()
This code makes me confused. How does it work?
Besides enabling await
, async
implicitly wraps the result of the function into a Promise.resolve()
. Roughly:
async function() {
return something;
}
Is equivalent to:
function() {
return Promise.resolve(something);
}
The thing is Promise.resolve()
"flattens" its argument, meaning if its argument is a thenable (such as another Promise) it automatically "resolves" to it. In other words, Promise.resolve(somethingThatIsAPromise).then(<work>)
has the same effect of somethingThatIsAPromise.then(<work>)
.
MDN tries to explain that behavior (bold is mine):
The
Promise.resolve()
method returns aPromise
object that is resolved with a given value. If the value is a promise, that promise is returned ; if the value is a thenable (ie has a "then
" method ), the returned promise will "follow" that thenable, adopting its eventual state; otherwise the returned promise will be fulfilled with the value. This function flattens nested layers of promise-like objects (eg a promise that resolves to a promise that resolves to something) into a single layer.
And, since what your arrow functions returns ( dataSources.userAPI.findOrCreateUser()
) is a Promise, due to that "flattening", having async
or not ends up in the same behavior.
The technical post webpages of this site follow the CC BY-SA 4.0 protocol. If you need to reprint, please indicate the site URL or the original address.Any question please contact:yoyou2525@163.com.