Using await outside of an async function
I was attempting to chain two async functions together, because the first had a conditional return parameter that caused the second to either run, or exit the module. However, I've found odd behavior I can't find in the specs.
async function isInLobby() {
//promise.all([chained methods here])
let exit = false;
if (someCondition) exit = true;
}
This is a bastardized snippet of my code (you can see the full scope here), that simply checks if a player if already in a lobby, but that's irrelevant.
Next we have this async function.
async function countPlayer() {
const keyLength = await scardAsync(game);
return keyLength;
}
This function doesn't need to run if exit === true.
I tried to do
const inLobby = await isInLobby();
This I hoped would await to results, so I can use inLobby to conditionally run countPlayer, however I received a typeerror with no specific details.
Why can't you await an async function outside of the scope of the function? I know it's a sugar promise, so it must be chained to then but why is it that in countPlayer I can await another promise, but outside, I can't await isInLobby?
await isInLobby(), and how inLobby is used? Also, where/how is countPlayer called?
isInLobby().then( … countPlayer().then … part, the solution is trivial: just make the function in which those calls are contained (the (req, res) => one) async.
await for your code at all? That's why I wondered that you accepted the answer that doesn't really relate to the problem in the question.
There is always this of course:
(async () => {
await ...
// all of the script....
})();
// nothing else
This makes a quick function with async where you can use await. It saves you the need to make an async function which is great! //credits Silve2611
Top level await is not supported. There are a few discussions by the standards committee on why this is, such as this Github issue.
There's also a thinkpiece on Github about why top level await is a bad idea. Specifically he suggests that if you have code like this:
// data.js
const data = await fetch( '/data.json' );
export default data;
Now any file that imports data.js won't execute until the fetch completes, so all of your module loading is now blocked. This makes it very difficult to reason about app module order, since we're used to top level Javascript executing synchronously and predictably. If this were allowed, knowing when a function gets defined becomes tricky.
My perspective is that it's bad practice for your module to have side effects simply by loading it. That means any consumer of your module will get side effects simply by requiring your module. This badly limits where your module can be used. A top level await probably means you're reading from some API or calling to some service at load time. Instead you should just export async functions that consumers can use at their own pace.
void async function() { const inLobby = await isInLobby() }()
inLobby to the function making it non-accessible?
.then() (sorry, should have made that a bit more clear).
As of Node.js 14.3.0, the top-level await is supported with a flag:
--experimental-top-level-await
As of Node.js 16.12.0 / 17.0.0, no flag required.
Further details: https://v8.dev/features/top-level-await.
you can do top level await since typescript 3.8
https://www.typescriptlang.org/docs/handbook/release-notes/typescript-3-8.html#-top-level-await
From the post:
This is because previously in JavaScript (along with most other languages with a similar feature), await was only allowed within the body of an async function. However, with top-level await, we can use await at the top level of a module.
const response = await fetch("...");
const greeting = await response.text();
console.log(greeting);
// Make sure we're a module
export {};
Note there’s a subtlety: top-level await only works at the top level of a module, and files are only considered modules when TypeScript finds an import or an export. In some basic cases, you might need to write out export {} as some boilerplate to make sure of this.
Top level await may not work in all environments where you might expect at this point. Currently, you can only use top level await when the target compiler option is es2017 or above, and module is esnext or system. Support within several environments and bundlers may be limited or may require enabling experimental support.
"type": "module" at the top of your package.json, or use the .jsm file extension.
.jsm has never been a valid file extension. It's .mjs.
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awaitthis anonymous function, which again, doesn't work from outside of functions.