I can't seem to wrap my head around why this does not work.
Because main
returns a promise; all async
functions do.
At the top level, you must either:
Use a top-level
async
function that never rejects (unless you want "unhandled rejection" errors), orUse
then
andcatch
, or(Coming soon!) Use top-level
await
, a proposal that has reached Stage 3 in the process that allows top-level use ofawait
in a module.
#1 - Top-level async
function that never rejects
(async () => {
try {
var text = await main();
console.log(text);
} catch (e) {
// Deal with the fact the chain failed
}
})();
Notice the catch
; you must handle promise rejections / async exceptions, since nothing else is going to; you have no caller to pass them on to. If you prefer, you could do that on the result of calling it via the catch
function (rather than try
/catch
syntax):
(async () => {
var text = await main();
console.log(text);
})().catch(e => {
// Deal with the fact the chain failed
});
...which is a bit more concise (I like it for that reason).
Or, of course, don't handle errors and just allow the "unhandled rejection" error.
#2 - then
and catch
main()
.then(text => {
console.log(text);
})
.catch(err => {
// Deal with the fact the chain failed
});
The catch
handler will be called if errors occur in the chain or in your then
handler. (Be sure your catch
handler doesn't throw errors, as nothing is registered to handle them.)
Or both arguments to then
:
main().then(
text => {
console.log(text);
},
err => {
// Deal with the fact the chain failed
}
);
Again notice we're registering a rejection handler. But in this form, be sure that neither of your then
callbacks doesn't throw any errors, nothing is registered to handle them.
#3 top-level await
in a module
You can't use await
at the top level of a non-module script, but the top-level await
proposal (Stage 3) allows you to use it at the top level of a module. It's similar to using a top-level async
function wrapper (#1 above) in that you don't want your top-level code to reject (throw an error) because that will result in an unhandled rejection error. So unless you want to have that unhandled rejection when things go wrong, as with #1, you'd want to wrap your code in an error handler:
// In a module, once the top-level `await` proposal lands
try {
var text = await main();
console.log(text);
} catch (e) {
// Deal with the fact the chain failed
}
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