On Wed, Sep 16, 2020 at 8:56 AM Yao Xiao <yao...@chromium.org> wrote:
>
> Hi v8-users,
>
> I'm new to v8.
>
> For a "script" that has a call to a sync function that returns an integer, I
> figured I could do the following to get the result in C++:
>
> v8::Local<v8::Value> result = script->Run(context).ToLocalChecked();
> int result_int = result->Int32Value(context).FromJust();
>
> I'm wondering if there's a way to get (i.e. make C++ aware of) the return
> value an async function? I tried to use await but it seems that the script
> won't compile.
You can attach your own .then and .catch callbacks if the script's
return value is a promise (which is what the return value of an async
function really is):
if (result->IsPromise()) {
Local<Promise> promise = result.As<Promise>();
if (promise->State() == Promise::kPending) {
Local<Function> resolve = Function::New(context,
Resolve).ToLocalChecked();
Local<Function> reject = Function::New(context, Reject).ToLocalChecked();
promise = promise.Then(resolve, reject).ToLocalChecked();
} else {
result = promise->Result(); // note: distinguish between
kFulfilled and kRejected
// ...
}
You'll need to pump the event loop and/or the microtask queue in order
for the promise to resolve.
Apropos the await keyword, that isn't accepted at the top-level scope
(outside an async function) unless you're executing the script as an
ES module and the --harmony_top_level_await flag is set.
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